com.unity.netcode.gameobjects@1.4.0

The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).

Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).

## [1.4.0] - 2023-04-10

### Added

- Added a way to access the GlobalObjectIdHash via PrefabIdHash for use in the Connection Approval Callback. (#2437)
- Added `OnServerStarted` and `OnServerStopped` events that will trigger only on the server (or host player) to notify that the server just started or is no longer active (#2420)
- Added `OnClientStarted` and `OnClientStopped` events that will trigger only on the client (or host player) to notify that the client just started or is no longer active (#2420)
- Added `NetworkTransform.UseHalfFloatPrecision` property that, when enabled, will use half float values for position, rotation, and scale. This yields a 50% bandwidth savings a the cost of precision. (#2388)
- Added `NetworkTransform.UseQuaternionSynchronization` property that, when enabled, will synchronize the entire quaternion. (#2388)
- Added `NetworkTransform.UseQuaternionCompression` property that, when enabled, will use a smallest three implementation reducing a full quaternion synchronization update to the size of an unsigned integer. (#2388)
- Added `NetworkTransform.SlerpPosition` property that, when enabled along with interpolation being enabled, will interpolate using `Vector3.Slerp`. (#2388)
- Added `BufferedLinearInterpolatorVector3` that replaces the float version, is now used by `NetworkTransform`, and provides the ability to enable or disable `Slerp`. (#2388)
- Added `HalfVector3` used for scale when half float precision is enabled. (#2388)
- Added `HalfVector4` used for rotation when half float precision and quaternion synchronization is enabled. (#2388)
- Added `HalfVector3DeltaPosition` used for position when half float precision is enabled. This handles loss in position precision by updating only the delta position as opposed to the full position. (#2388)
- Added `NetworkTransform.GetSpaceRelativePosition` and `NetworkTransform.GetSpaceRelativeRotation` helper methods to return the proper values depending upon whether local or world space. (#2388)
- Added `NetworkTransform.OnAuthorityPushTransformState` virtual method that is invoked just prior to sending the `NetworkTransformState` to non-authoritative instances. This provides users with the ability to obtain more precise delta values for prediction related calculations. (#2388)
- Added `NetworkTransform.OnNetworkTransformStateUpdated` virtual method that is invoked just after the authoritative `NetworkTransformState` is applied. This provides users with the ability to obtain more precise delta values for prediction related calculations. (#2388)
- Added `NetworkTransform.OnInitialize`virtual method that is invoked after the `NetworkTransform` has been initialized or re-initialized when ownership changes. This provides for a way to make adjustments when `NetworkTransform` is initialized (i.e. resetting client prediction etc) (#2388)
- Added `NetworkObject.SynchronizeTransform` property (default is true) that provides users with another way to help with bandwidth optimizations where, when set to false, the `NetworkObject`'s associated transform will not be included when spawning and/or synchronizing late joining players. (#2388)
- Added `NetworkSceneManager.ActiveSceneSynchronizationEnabled` property, disabled by default, that enables client synchronization of server-side active scene changes. (#2383)
- Added `NetworkObject.ActiveSceneSynchronization`, disabled by default, that will automatically migrate a `NetworkObject` to a newly assigned active scene. (#2383)
- Added `NetworkObject.SceneMigrationSynchronization`, enabled by default, that will synchronize client(s) when a `NetworkObject` is migrated into a new scene on the server side via `SceneManager.MoveGameObjectToScene`. (#2383)

### Changed

- Made sure the `CheckObjectVisibility` delegate is checked and applied, upon `NetworkShow` attempt. Found while supporting (#2454), although this is not a fix for this (already fixed) issue. (#2463)
- Changed `NetworkTransform` authority handles delta checks on each new network tick and no longer consumes processing cycles checking for deltas for all frames in-between ticks. (#2388)
- Changed the `NetworkTransformState` structure is now public and now has public methods that provide access to key properties of the `NetworkTransformState` structure. (#2388)
- Changed `NetworkTransform` interpolation adjusts its interpolation "ticks ago" to be 2 ticks latent if it is owner authoritative and the instance is not the server or 1 tick latent if the instance is the server and/or is server authoritative. (#2388)
- Updated `NetworkSceneManager` to migrate dynamically spawned `NetworkObject`s with `DestroyWithScene` set to false into the active scene if their current scene is unloaded. (#2383)
- Updated the server to synchronize its local `NetworkSceneManager.ClientSynchronizationMode` during the initial client synchronization. (#2383)

### Fixed

- Fixed issue where during client synchronization the synchronizing client could receive a ObjectSceneChanged message before the client-side NetworkObject instance had been instantiated and spawned. (#2502)
- Fixed issue where `NetworkAnimator` was building client RPC parameters to exclude the host from sending itself messages but was not including it in the ClientRpc parameters. (#2492)
- Fixed issue where `NetworkAnimator` was not properly detecting and synchronizing cross fade initiated transitions. (#2481)
- Fixed issue where `NetworkAnimator` was not properly synchronizing animation state updates. (#2481)
- Fixed float NetworkVariables not being rendered properly in the inspector of NetworkObjects. (#2441)
- Fixed an issue where Named Message Handlers could remove themselves causing an exception when the metrics tried to access the name of the message.(#2426)
- Fixed registry of public `NetworkVariable`s in derived `NetworkBehaviour`s (#2423)
- Fixed issue where runtime association of `Animator` properties to `AnimationCurve`s would cause `NetworkAnimator` to attempt to update those changes. (#2416)
- Fixed issue where `NetworkAnimator` would not check if its associated `Animator` was valid during serialization and would spam exceptions in the editor console. (#2416)
- Fixed issue with a child's rotation rolling over when interpolation is enabled on a `NetworkTransform`. Now using half precision or full quaternion synchronization will always update all axis. (#2388)
- Fixed issue where `NetworkTransform` was not setting the teleport flag when the `NetworkTransform.InLocalSpace` value changed. This issue only impacted `NetworkTransform` when interpolation was enabled. (#2388)
- Fixed issue when the `NetworkSceneManager.ClientSynchronizationMode` is `LoadSceneMode.Additive` and the server changes the currently active scene prior to a client connecting then upon a client connecting and being synchronized the NetworkSceneManager would clear its internal ScenePlacedObjects list that could already be populated. (#2383)
- Fixed issue where a client would load duplicate scenes of already preloaded scenes during the initial client synchronization and `NetworkSceneManager.ClientSynchronizationMode` was set to `LoadSceneMode.Additive`. (#2383)

CHANGELOG.md

@@ -6,6 +6,205 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 Additional documentation and release notes are available at [Multiplayer Documentation](https://docs-multiplayer.unity3d.com).
 
+## [1.4.0] - 2023-04-10
+
+### Added
+
+- Added a way to access the GlobalObjectIdHash via PrefabIdHash for use in the Connection Approval Callback. (#2437)
+- Added `OnServerStarted` and `OnServerStopped` events that will trigger only on the server (or host player) to notify that the server just started or is no longer active (#2420)
+- Added `OnClientStarted` and `OnClientStopped` events that will trigger only on the client (or host player) to notify that the client just started or is no longer active (#2420)
+- Added `NetworkTransform.UseHalfFloatPrecision` property that, when enabled, will use half float values for position, rotation, and scale. This yields a 50% bandwidth savings a the cost of precision. (#2388)
+- Added `NetworkTransform.UseQuaternionSynchronization` property that, when enabled, will synchronize the entire quaternion. (#2388)
+- Added `NetworkTransform.UseQuaternionCompression` property that, when enabled, will use a smallest three implementation reducing a full quaternion synchronization update to the size of an unsigned integer. (#2388)
+- Added `NetworkTransform.SlerpPosition` property that, when enabled along with interpolation being enabled, will interpolate using `Vector3.Slerp`. (#2388)
+- Added `BufferedLinearInterpolatorVector3` that replaces the float version, is now used by `NetworkTransform`, and provides the ability to enable or disable `Slerp`. (#2388)
+- Added `HalfVector3` used for scale when half float precision is enabled. (#2388)
+- Added `HalfVector4` used for rotation when half float precision and quaternion synchronization is enabled. (#2388)
+- Added `HalfVector3DeltaPosition` used for position when half float precision is enabled. This handles loss in position precision by updating only the delta position as opposed to the full position. (#2388)
+- Added `NetworkTransform.GetSpaceRelativePosition` and `NetworkTransform.GetSpaceRelativeRotation` helper methods to return the proper values depending upon whether local or world space. (#2388)
+- Added `NetworkTransform.OnAuthorityPushTransformState` virtual method that is invoked just prior to sending the `NetworkTransformState` to non-authoritative instances. This provides users with the ability to obtain more precise delta values for prediction related calculations. (#2388)
+- Added `NetworkTransform.OnNetworkTransformStateUpdated` virtual method that is invoked just after the authoritative `NetworkTransformState` is applied. This provides users with the ability to obtain more precise delta values for prediction related calculations. (#2388)
+- Added `NetworkTransform.OnInitialize`virtual method that is invoked after the `NetworkTransform` has been initialized or re-initialized when ownership changes. This provides for a way to make adjustments when `NetworkTransform` is initialized (i.e. resetting client prediction etc) (#2388)
+- Added `NetworkObject.SynchronizeTransform` property (default is true) that provides users with another way to help with bandwidth optimizations where, when set to false, the `NetworkObject`'s associated transform will not be included when spawning and/or synchronizing late joining players. (#2388)
+- Added `NetworkSceneManager.ActiveSceneSynchronizationEnabled` property, disabled by default, that enables client synchronization of server-side active scene changes. (#2383)
+- Added `NetworkObject.ActiveSceneSynchronization`, disabled by default, that will automatically migrate a `NetworkObject` to a newly assigned active scene. (#2383)
+- Added `NetworkObject.SceneMigrationSynchronization`, enabled by default, that will synchronize client(s) when a `NetworkObject` is migrated into a new scene on the server side via `SceneManager.MoveGameObjectToScene`. (#2383)
+
+### Changed
+
+- Made sure the `CheckObjectVisibility` delegate is checked and applied, upon `NetworkShow` attempt. Found while supporting (#2454), although this is not a fix for this (already fixed) issue. (#2463)
+- Changed `NetworkTransform` authority handles delta checks on each new network tick and no longer consumes processing cycles checking for deltas for all frames in-between ticks. (#2388)
+- Changed the `NetworkTransformState` structure is now public and now has public methods that provide access to key properties of the `NetworkTransformState` structure. (#2388)
+- Changed `NetworkTransform` interpolation adjusts its interpolation "ticks ago" to be 2 ticks latent if it is owner authoritative and the instance is not the server or 1 tick latent if the instance is the server and/or is server authoritative. (#2388)
+- Updated `NetworkSceneManager` to migrate dynamically spawned `NetworkObject`s with `DestroyWithScene` set to false into the active scene if their current scene is unloaded. (#2383)
+- Updated the server to synchronize its local `NetworkSceneManager.ClientSynchronizationMode` during the initial client synchronization. (#2383)
+
+### Fixed
+
+- Fixed issue where during client synchronization the synchronizing client could receive a ObjectSceneChanged message before the client-side NetworkObject instance had been instantiated and spawned. (#2502)
+- Fixed issue where `NetworkAnimator` was building client RPC parameters to exclude the host from sending itself messages but was not including it in the ClientRpc parameters. (#2492)
+- Fixed issue where `NetworkAnimator` was not properly detecting and synchronizing cross fade initiated transitions. (#2481)
+- Fixed issue where `NetworkAnimator` was not properly synchronizing animation state updates. (#2481)
+- Fixed float NetworkVariables not being rendered properly in the inspector of NetworkObjects. (#2441)
+- Fixed an issue where Named Message Handlers could remove themselves causing an exception when the metrics tried to access the name of the message.(#2426)
+- Fixed registry of public `NetworkVariable`s in derived `NetworkBehaviour`s (#2423)
+- Fixed issue where runtime association of `Animator` properties to `AnimationCurve`s would cause `NetworkAnimator` to attempt to update those changes. (#2416)
+- Fixed issue where `NetworkAnimator` would not check if its associated `Animator` was valid during serialization and would spam exceptions in the editor console. (#2416)
+- Fixed issue with a child's rotation rolling over when interpolation is enabled on a `NetworkTransform`. Now using half precision or full quaternion synchronization will always update all axis. (#2388)
+- Fixed issue where `NetworkTransform` was not setting the teleport flag when the `NetworkTransform.InLocalSpace` value changed. This issue only impacted `NetworkTransform` when interpolation was enabled. (#2388)
+- Fixed issue when the `NetworkSceneManager.ClientSynchronizationMode` is `LoadSceneMode.Additive` and the server changes the currently active scene prior to a client connecting then upon a client connecting and being synchronized the NetworkSceneManager would clear its internal ScenePlacedObjects list that could already be populated. (#2383)
+- Fixed issue where a client would load duplicate scenes of already preloaded scenes during the initial client synchronization and `NetworkSceneManager.ClientSynchronizationMode` was set to `LoadSceneMode.Additive`. (#2383)
+
+## [1.3.1] - 2023-03-27
+
+### Added
+
+- Added detection and graceful handling of corrupt packets for additional safety. (#2419)
+
+### Changed
+
+- The UTP component UI has been updated to be more user-friendly for new users by adding a simple toggle to switch between local-only (127.0.0.1) and remote (0.0.0.0) binding modes, using the toggle "Allow Remote Connections" (#2408)
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.3. (#2450)
+- `NetworkShow()` of `NetworkObject`s are delayed until the end of the frame to ensure consistency of delta-driven variables like `NetworkList`.
+- Dirty `NetworkObject` are reset at end-of-frame and not at serialization time.
+- `NetworkHide()` of an object that was just `NetworkShow()`n produces a warning, as remote clients will _not_ get a spawn/despawn pair.
+- Renamed the NetworkTransform.SetState parameter `shouldGhostsInterpolate` to `teleportDisabled` for better clarity of what that parameter does. (#2228)
+- Network prefabs are now stored in a ScriptableObject that can be shared between NetworkManagers, and have been exposed for public access. By default, a Default Prefabs List is created that contains all NetworkObject prefabs in the project, and new NetworkManagers will default to using that unless that option is turned off in the Netcode for GameObjects settings. Existing NetworkManagers will maintain their existing lists, which can be migrated to the new format via a button in their inspector. (#2322)
+
+### Fixed
+
+- Fixed issue where changes to a layer's weight would not synchronize unless a state transition was occurring.(#2399)
+- Fixed issue where `NetworkManager.LocalClientId` was returning the `NetworkTransport.ServerClientId` as opposed to the `NetworkManager.m_LocalClientId`. (#2398)
+- Fixed issue where a dynamically spawned `NetworkObject` parented under an in-scene placed `NetworkObject` would have its `InScenePlaced` value changed to `true`. This would result in a soft synchronization error for late joining clients. (#2396)
+- Fixed a UTP test that was failing when you install Unity Transport package 2.0.0 or newer. (#2347)
+- Fixed issue where `NetcodeSettingsProvider` would throw an exception in Unity 2020.3.x versions. (#2345)
+- Fixed server side issue where, depending upon component ordering, some NetworkBehaviour components might not have their OnNetworkDespawn method invoked if the client side disconnected. (#2323)
+- Fixed a case where data corruption could occur when using UnityTransport when reaching a certain level of send throughput. (#2332)
+- Fixed an issue in `UnityTransport` where an exception would be thrown if starting a Relay host/server on WebGL. This exception should only be thrown if using direct connections (where WebGL can't act as a host/server). (#2321)
+- Fixed `NetworkAnimator` issue where it was not checking for `AnimatorStateTtansition.destinationStateMachine` and any possible sub-states defined within it. (#2309)
+- Fixed `NetworkAnimator` issue where the host client was receiving the ClientRpc animation updates when the host was the owner.(#2309)
+- Fixed `NetworkAnimator` issue with using pooled objects and when specific properties are cleaned during despawn and destroy.(#2309)
+- Fixed issue where `NetworkAnimator` was checking for animation changes when the associated `NetworkObject` was not spawned.(#2309)
+- Corrected an issue with the documentation for BufferSerializer (#2401)
+
+## [1.2.0] - 2022-11-21
+
+### Added
+
+- Added protected method `NetworkBehaviour.OnSynchronize` which is invoked during the initial `NetworkObject` synchronization process. This provides users the ability to include custom serialization information that will be applied to the `NetworkBehaviour` prior to the `NetworkObject` being spawned. (#2298)
+- Added support for different versions of the SDK to talk to each other in circumstances where changes permit it. Starting with this version and into future versions, patch versions should be compatible as long as the minor version is the same. (#2290)
+- Added `NetworkObject` auto-add helper and Multiplayer Tools install reminder settings to Project Settings. (#2285)
+- Added `public string DisconnectReason` getter to `NetworkManager` and `string Reason` to `ConnectionApprovalResponse`. Allows connection approval to communicate back a reason. Also added `public void DisconnectClient(ulong clientId, string reason)` allowing setting a disconnection reason, when explicitly disconnecting a client. (#2280)
+
+### Changed
+
+- Changed 3rd-party `XXHash` (32 & 64) implementation with an in-house reimplementation (#2310)
+- When `NetworkConfig.EnsureNetworkVariableLengthSafety` is disabled `NetworkVariable` fields do not write the additional `ushort` size value (_which helps to reduce the total synchronization message size_), but when enabled it still writes the additional `ushort` value. (#2298)
+- Optimized bandwidth usage by encoding most integer fields using variable-length encoding. (#2276)
+
+### Fixed
+- Fixed `IsSpawnedObjectsPendingInDontDestroyOnLoad` is only set to true when loading a scene using `LoadSceneMode.Singleonly`. (#2330)
+- Fixed issue where `NetworkTransform` components nested under a parent with a `NetworkObject` component  (i.e. network prefab) would not have their associated `GameObject`'s transform synchronized. (#2298)
+- Fixed issue where `NetworkObject`s that failed to instantiate could cause the entire synchronization pipeline to be disrupted/halted for a connecting client. (#2298)
+- Fixed issue where in-scene placed `NetworkObject`s nested under a `GameObject` would be added to the orphaned children list causing continual console warning log messages. (#2298)
+- Custom messages are now properly received by the local client when they're sent while running in host mode. (#2296)
+- Fixed issue where the host would receive more than one event completed notification when loading or unloading a scene only when no clients were connected. (#2292)
+- Fixed an issue in `UnityTransport` where an error would be logged if the 'Use Encryption' flag was enabled with a Relay configuration that used a secure protocol. (#2289)
+- Fixed issue where in-scene placed `NetworkObjects` were not honoring the `AutoObjectParentSync` property. (#2281)
+- Fixed the issue where `NetworkManager.OnClientConnectedCallback` was being invoked before in-scene placed `NetworkObject`s had been spawned when starting `NetworkManager` as a host. (#2277)
+- Creating a `FastBufferReader` with `Allocator.None` will not result in extra memory being allocated for the buffer (since it's owned externally in that scenario). (#2265)
+
+### Removed
+
+- Removed the `NetworkObject` auto-add and Multiplayer Tools install reminder settings from the Menu interface. (#2285)
+
+## [1.1.0] - 2022-10-21
+
+### Added
+
+- Added `NetworkManager.IsApproved` flag that is set to `true` a client has been approved.(#2261)
+- `UnityTransport` now provides a way to set the Relay server data directly from the `RelayServerData` structure (provided by the Unity Transport package) throuh its `SetRelayServerData` method. This allows making use of the new APIs in UTP 1.3 that simplify integration of the Relay SDK. (#2235)
+- IPv6 is now supported for direct connections when using `UnityTransport`. (#2232)
+- Added WebSocket support when using UTP 2.0 with `UseWebSockets` property in the `UnityTransport` component of the `NetworkManager` allowing to pick WebSockets for communication. When building for WebGL, this selection happens automatically. (#2201)
+- Added position, rotation, and scale to the `ParentSyncMessage` which provides users the ability to specify the final values on the server-side when `OnNetworkObjectParentChanged` is invoked just before the message is created (when the `Transform` values are applied to the message). (#2146)
+- Added `NetworkObject.TryRemoveParent` method for convenience purposes opposed to having to cast null to either `GameObject` or `NetworkObject`. (#2146)
+
+### Changed
+
+- Updated `UnityTransport` dependency on `com.unity.transport` to 1.3.0. (#2231)
+- The send queues of `UnityTransport` are now dynamically-sized. This means that there shouldn't be any need anymore to tweak the 'Max Send Queue Size' value. In fact, this field is now removed from the inspector and will not be serialized anymore. It is still possible to set it manually using the `MaxSendQueueSize` property, but it is not recommended to do so aside from some specific needs (e.g. limiting the amount of memory used by the send queues in very constrained environments). (#2212)
+- As a consequence of the above change, the `UnityTransport.InitialMaxSendQueueSize` field is now deprecated. There is no default value anymore since send queues are dynamically-sized. (#2212)
+- The debug simulator in `UnityTransport` is now non-deterministic. Its random number generator used to be seeded with a constant value, leading to the same pattern of packet drops, delays, and jitter in every run. (#2196)
+- `NetworkVariable<>` now supports managed `INetworkSerializable` types, as well as other managed types with serialization/deserialization delegates registered to `UserNetworkVariableSerialization<T>.WriteValue` and `UserNetworkVariableSerialization<T>.ReadValue` (#2219)
+- `NetworkVariable<>` and `BufferSerializer<BufferSerializerReader>` now deserialize `INetworkSerializable` types in-place, rather than constructing new ones. (#2219)
+
+### Fixed
+
+- Fixed `NetworkManager.ApprovalTimeout` will not timeout due to slower client synchronization times as it now uses the added `NetworkManager.IsApproved` flag to determined if the client has been approved or not.(#2261)
+- Fixed issue caused when changing ownership of objects hidden to some clients (#2242)
+- Fixed issue where an in-scene placed NetworkObject would not invoke NetworkBehaviour.OnNetworkSpawn if the GameObject was disabled when it was despawned. (#2239)
+- Fixed issue where clients were not rebuilding the `NetworkConfig` hash value for each unique connection request. (#2226)
+- Fixed the issue where player objects were not taking the `DontDestroyWithOwner` property into consideration when a client disconnected. (#2225)
+- Fixed issue where `SceneEventProgress` would not complete if a client late joins while it is still in progress. (#2222)
+- Fixed issue where `SceneEventProgress` would not complete if a client disconnects. (#2222)
+- Fixed issues with detecting if a `SceneEventProgress` has timed out. (#2222)
+- Fixed issue #1924 where `UnityTransport` would fail to restart after a first failure (even if what caused the initial failure was addressed). (#2220)
+- Fixed issue where `NetworkTransform.SetStateServerRpc` and `NetworkTransform.SetStateClientRpc` were not honoring local vs world space settings when applying the position and rotation. (#2203)
+- Fixed ILPP `TypeLoadException` on WebGL on MacOS Editor and potentially other platforms. (#2199)
+- Implicit conversion of NetworkObjectReference to GameObject will now return null instead of throwing an exception if the referenced object could not be found (i.e., was already despawned) (#2158)
+- Fixed warning resulting from a stray NetworkAnimator.meta file (#2153)
+- Fixed Connection Approval Timeout not working client side. (#2164)
+- Fixed issue where the `WorldPositionStays` parenting parameter was not being synchronized with clients. (#2146)
+- Fixed issue where parented in-scene placed `NetworkObject`s would fail for late joining clients. (#2146)
+- Fixed issue where scale was not being synchronized which caused issues with nested parenting and scale when `WorldPositionStays` was true. (#2146)
+- Fixed issue with `NetworkTransform.ApplyTransformToNetworkStateWithInfo` where it was not honoring axis sync settings when `NetworkTransformState.IsTeleportingNextFrame` was true. (#2146)
+- Fixed issue with `NetworkTransform.TryCommitTransformToServer` where it was not honoring the `InLocalSpace` setting. (#2146)
+- Fixed ClientRpcs always reporting in the profiler view as going to all clients, even when limited to a subset of clients by `ClientRpcParams`. (#2144)
+- Fixed RPC codegen failing to choose the correct extension methods for `FastBufferReader` and `FastBufferWriter` when the parameters were a generic type (i.e., List<int>) and extensions for multiple instantiations of that type have been defined (i.e., List<int> and List<string>) (#2142)
+- Fixed the issue where running a server (i.e. not host) the second player would not receive updates (unless a third player joined). (#2127)
+- Fixed issue where late-joining client transition synchronization could fail when more than one transition was occurring.(#2127)
+- Fixed throwing an exception in `OnNetworkUpdate` causing other `OnNetworkUpdate` calls to not be executed. (#1739)
+- Fixed synchronization when Time.timeScale is set to 0. This changes timing update to use unscaled deltatime. Now network updates rate are independent from the local time scale. (#2171)
+- Fixed not sending all NetworkVariables to all clients when a client connects to a server. (#1987)
+- Fixed IsOwner/IsOwnedByServer being wrong on the server after calling RemoveOwnership (#2211)
+
+## [1.0.2] - 2022-09-12
+
+### Fixed
+
+- Fixed issue where `NetworkTransform` was not honoring the InLocalSpace property on the authority side during OnNetworkSpawn. (#2170)
+- Fixed issue where `NetworkTransform` was not ending extrapolation for the previous state causing non-authoritative instances to become out of synch. (#2170)
+- Fixed issue where `NetworkTransform` was not continuing to interpolate for the remainder of the associated tick period. (#2170)
+- Fixed issue during `NetworkTransform.OnNetworkSpawn` for non-authoritative instances where it was initializing interpolators with the replicated network state which now only contains the transform deltas that occurred during a network tick and not the entire transform state. (#2170)
+
+## [1.0.1] - 2022-08-23
+
+### Changed
+
+- Changed version to 1.0.1. (#2131)
+- Updated dependency on `com.unity.transport` to 1.2.0. (#2129)
+- When using `UnityTransport`, _reliable_ payloads are now allowed to exceed the configured 'Max Payload Size'. Unreliable payloads remain bounded by this setting. (#2081)
+- Performance improvements for cases with large number of NetworkObjects, by not iterating over all unchanged NetworkObjects
+
+### Fixed
+
+- Fixed an issue where reading/writing more than 8 bits at a time with BitReader/BitWriter would write/read from the wrong place, returning and incorrect result. (#2130)
+- Fixed issue with the internal `NetworkTransformState.m_Bitset` flag not getting cleared upon the next tick advancement. (#2110)
+- Fixed interpolation issue with `NetworkTransform.Teleport`. (#2110)
+- Fixed issue where the authoritative side was interpolating its transform. (#2110)
+- Fixed Owner-written NetworkVariable infinitely write themselves (#2109)
+- Fixed NetworkList issue that showed when inserting at the very end of a NetworkList (#2099)
+- Fixed issue where a client owner of a `NetworkVariable` with both owner read and write permissions would not update the server side when changed. (#2097)
+- Fixed issue when attempting to spawn a parent `GameObject`, with `NetworkObject` component attached, that has one or more child `GameObject`s, that are inactive in the hierarchy, with `NetworkBehaviour` components it will no longer attempt to spawn the associated `NetworkBehaviour`(s) or invoke ownership changed notifications but will log a warning message. (#2096)
+- Fixed an issue where destroying a NetworkBehaviour would not deregister it from the parent NetworkObject, leading to exceptions when the parent was later destroyed. (#2091)
+- Fixed issue where `NetworkObject.NetworkHide` was despawning and destroying, as opposed to only despawning, in-scene placed `NetworkObject`s. (#2086)
+- Fixed `NetworkAnimator` synchronizing transitions twice due to it detecting the change in animation state once a transition is started by a trigger. (#2084)
+- Fixed issue where `NetworkAnimator` would not synchronize a looping animation for late joining clients if it was at the very end of its loop. (#2076)
+- Fixed issue where `NetworkAnimator` was not removing its subscription from `OnClientConnectedCallback` when despawned during the shutdown sequence. (#2074)
+- Fixed IsServer and IsClient being set to false before object despawn during the shutdown sequence. (#2074)
+- Fixed NetworkList Value event on the server. PreviousValue is now set correctly when a new value is set through property setter. (#2067)
+- Fixed NetworkLists not populating on client. NetworkList now uses the most recent list as opposed to the list at the end of previous frame, when sending full updates to dynamically spawned NetworkObject. The difference in behaviour is required as scene management spawns those objects at a different time in the frame, relative to updates. (#2062)
+
 ## [1.0.0] - 2022-06-27
 
 ### Changed
@@ -69,6 +268,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `ClientNetworkTransform` from the package samples and moved to Boss Room's Utilities package which can be found [here](https://github.com/Unity-Technologies/com.unity.multiplayer.samples.coop/blob/main/Packages/com.unity.multiplayer.samples.coop/Utilities/Net/ClientAuthority/ClientNetworkTransform.cs) (#1912)
 
 ### Fixed
+
 - Fixed issue where `NetworkSceneManager` did not synchronize despawned in-scene placed NetworkObjects. (#1898)
 - Fixed `NetworkTransform` generating false positive rotation delta checks when rolling over between 0 and 360 degrees. (#1890)
 - Fixed client throwing an exception if it has messages in the outbound queue when processing the `NetworkEvent.Disconnect` event and is using UTP. (#1884)
@@ -122,10 +322,12 @@ Additional documentation and release notes are available at [Multiplayer Documen
 ## [1.0.0-pre.6] - 2022-03-02
 
 ### Added
+
 - NetworkAnimator now properly synchrhonizes all animation layers as well as runtime-adjusted weighting between them (#1765)
 - Added first set of tests for NetworkAnimator - parameter syncing, trigger set / reset, override network animator (#1735)
 
 ### Fixed
+
 - Fixed an issue where sometimes the first client to connect to the server could see messages from the server as coming from itself. (#1683)
 - Fixed an issue where clients seemed to be able to send messages to ClientId 1, but these messages would actually still go to the server (id 0) instead of that client. (#1683)
 - Improved clarity of error messaging when a client attempts to send a message to a destination other than the server, which isn't allowed. (#1683)
@@ -177,6 +379,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Removed `FixedQueue`, `StreamExtensions`, `TypeExtensions` (#1398)
 
 ### Fixed
+
 - Fixed in-scene NetworkObjects that are moved into the DDOL scene not getting restored to their original active state (enabled/disabled) after a full scene transition (#1354)
 - Fixed invalid IL code being generated when using `this` instead of `this ref` for the FastBufferReader/FastBufferWriter parameter of an extension method. (#1393)
 - Fixed an issue where if you are running as a server (not host) the LoadEventCompleted and UnloadEventCompleted events would fire early by the NetworkSceneManager (#1379)
@@ -191,6 +394,7 @@ Additional documentation and release notes are available at [Multiplayer Documen
 - Fixed network tick value sometimes being duplicated or skipped. (#1614)
 
 ### Changed
+
 - The SDK no longer limits message size to 64k. (The transport may still impose its own limits, but the SDK no longer does.) (#1384)
 - Updated com.unity.collections to 1.1.0 (#1451)
 - NetworkManager's GameObject is no longer allowed to be nested under one or more GameObject(s).(#1484)

Components/AssemblyInfo.cs

@@ -1,10 +1,15 @@
 using System.Runtime.CompilerServices;
 
 #if UNITY_EDITOR
-[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#endif // UNITY_EDITOR
-#endif
+
+#if UNITY_INCLUDE_TESTS
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#endif // UNITY_INCLUDE_TESTS

Components/HalfVector3.cs

@@ -0,0 +1,159 @@
+using System.Runtime.CompilerServices;
+using Unity.Mathematics;
+using UnityEngine;
+
+namespace Unity.Netcode.Components
+{
+    /// <summary>
+    /// Half float precision <see cref="Vector3"/>.
+    /// </summary>
+    /// <remarks>
+    /// The Vector3T<ushort> values are half float values returned by <see cref="Mathf.FloatToHalf(float)"/> for each
+    /// individual axis and the 16 bits of the half float are stored as <see cref="ushort"/> values since C# does not have
+    /// a half float type.
+    /// </remarks>
+    public struct HalfVector3 : INetworkSerializable
+    {
+        internal const int Length = 3;
+
+        /// <summary>
+        /// The half float precision value of the x-axis as a <see cref="half"/>.
+        /// </summary>
+        public half X => Axis.x;
+        /// <summary>
+        /// The half float precision value of the y-axis as a <see cref="half"/>.
+        /// </summary>
+        public half Y => Axis.y;
+        /// <summary>
+        /// The half float precision value of the z-axis as a <see cref="half"/>.
+        /// </summary>
+        public half Z => Axis.x;
+
+        /// <summary>
+        /// Used to store the half float precision values as a <see cref="half3"/>
+        /// </summary>
+        public half3 Axis;
+
+        /// <summary>
+        /// Determine which axis will be synchronized during serialization
+        /// </summary>
+        public bool3 AxisToSynchronize;
+
+        private void SerializeWrite(FastBufferWriter writer)
+        {
+            for (int i = 0; i < Length; i++)
+            {
+                if (AxisToSynchronize[i])
+                {
+                    writer.WriteUnmanagedSafe(Axis[i]);
+                }
+            }
+        }
+
+        private void SerializeRead(FastBufferReader reader)
+        {
+            for (int i = 0; i < Length; i++)
+            {
+                if (AxisToSynchronize[i])
+                {
+                    var axisValue = Axis[i];
+                    reader.ReadUnmanagedSafe(out axisValue);
+                    Axis[i] = axisValue;
+                }
+            }
+        }
+
+        /// <summary>
+        /// The serialization implementation of <see cref="INetworkSerializable"/>.
+        /// </summary>
+        public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+            if (serializer.IsReader)
+            {
+                SerializeRead(serializer.GetFastBufferReader());
+            }
+            else
+            {
+                SerializeWrite(serializer.GetFastBufferWriter());
+            }
+        }
+
+        /// <summary>
+        /// Gets the full precision value as a <see cref="Vector3"/>.
+        /// </summary>
+        /// <returns>a <see cref="Vector3"/> as the full precision value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 ToVector3()
+        {
+            Vector3 fullPrecision = Vector3.zero;
+            Vector3 fullConversion = math.float3(Axis);
+            for (int i = 0; i < Length; i++)
+            {
+                if (AxisToSynchronize[i])
+                {
+                    fullPrecision[i] = fullConversion[i];
+                }
+            }
+            return fullPrecision;
+        }
+
+        /// <summary>
+        /// Converts a full precision <see cref="Vector3"/> to half precision and updates the current instance.
+        /// </summary>
+        /// <param name="vector3">The <see cref="Vector3"/> to convert.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void UpdateFrom(ref Vector3 vector3)
+        {
+            var half3Full = math.half3(vector3);
+            for (int i = 0; i < Length; i++)
+            {
+                if (AxisToSynchronize[i])
+                {
+                    Axis[i] = half3Full[i];
+                }
+            }
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="vector3">The initial axial values (converted to half floats) when instantiated.</param>
+        /// <param name="vector3AxisToSynchronize">The axis to synchronize.</param>
+        public HalfVector3(Vector3 vector3, bool3 axisToSynchronize)
+        {
+            Axis = half3.zero;
+            AxisToSynchronize = axisToSynchronize;
+            UpdateFrom(ref vector3);
+        }
+
+        /// <summary>
+        /// Constructor that defaults to all axis being synchronized.
+        /// </summary>
+        /// <param name="vector3">The initial axial values (converted to half floats) when instantiated.</param>
+        public HalfVector3(Vector3 vector3) : this(vector3, math.bool3(true))
+        {
+
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="x">The initial x axis (converted to half float) value when instantiated.</param>
+        /// <param name="y">The initial y axis (converted to half float) value when instantiated.</param>
+        /// <param name="z">The initial z axis (converted to half float) value when instantiated.</param>
+        /// <param name="axisToSynchronize">The axis to synchronize.</param>
+        public HalfVector3(float x, float y, float z, bool3 axisToSynchronize) : this(new Vector3(x, y, z), axisToSynchronize)
+        {
+        }
+
+        /// <summary>
+        /// Constructor that defaults to all axis being synchronized.
+        /// </summary>
+        /// <param name="x">The initial x axis (converted to half float) value when instantiated.</param>
+        /// <param name="y">The initial y axis (converted to half float) value when instantiated.</param>
+        /// <param name="z">The initial z axis (converted to half float) value when instantiated.</param>
+        public HalfVector3(float x, float y, float z) : this(new Vector3(x, y, z), math.bool3(true))
+        {
+        }
+    }
+}

Components/HalfVector3.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: c2e5a740c1abd4315801e3f26ecf8adb
+guid: b0e371533eaeac446b16b10886f64f84
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Components/HalfVector4.cs

@@ -0,0 +1,137 @@
+using System.Runtime.CompilerServices;
+using Unity.Mathematics;
+using UnityEngine;
+
+namespace Unity.Netcode.Components
+{
+    /// <summary>
+    /// Half Precision <see cref="Vector4"/> that can also be used to convert a <see cref="Quaternion"/> to half precision.
+    /// </summary>
+    /// <remarks>
+    /// The Vector4T<ushort> values are half float values returned by <see cref="Mathf.FloatToHalf(float)"/> for each
+    /// individual axis and the 16 bits of the half float are stored as <see cref="ushort"/> values since C# does not have
+    /// a half float type.
+    /// </remarks>
+    public struct HalfVector4 : INetworkSerializable
+    {
+        internal const int Length = 4;
+        /// <summary>
+        /// The half float precision value of the x-axis as a <see cref="half"/>.
+        /// </summary>
+        public half X => Axis.x;
+
+        /// <summary>
+        /// The half float precision value of the y-axis as a <see cref="half"/>.
+        /// </summary>
+        public half Y => Axis.y;
+
+        /// <summary>
+        /// The half float precision value of the z-axis as a <see cref="half"/>.
+        /// </summary>
+        public half Z => Axis.z;
+
+        /// <summary>
+        /// The half float precision value of the w-axis as a <see cref="half"/>.
+        /// </summary>
+        public half W => Axis.w;
+
+        /// <summary>
+        /// Used to store the half float precision values as a <see cref="half4"/>
+        /// </summary>
+        public half4 Axis;
+
+        private void SerializeWrite(FastBufferWriter writer)
+        {
+            for (int i = 0; i < Length; i++)
+            {
+                writer.WriteUnmanagedSafe(Axis[i]);
+            }
+        }
+
+        private void SerializeRead(FastBufferReader reader)
+        {
+            for (int i = 0; i < Length; i++)
+            {
+                var axisValue = Axis[i];
+                reader.ReadUnmanagedSafe(out axisValue);
+                Axis[i] = axisValue;
+            }
+        }
+
+        /// <summary>
+        /// The serialization implementation of <see cref="INetworkSerializable"/>.
+        /// </summary>
+        public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+            if (serializer.IsReader)
+            {
+                SerializeRead(serializer.GetFastBufferReader());
+            }
+            else
+            {
+                SerializeWrite(serializer.GetFastBufferWriter());
+            }
+        }
+
+        /// <summary>
+        /// Converts this instance to a full precision <see cref="Vector4"/>.
+        /// </summary>
+        /// <returns>A <see cref="Vector4"/> as the full precision value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector4 ToVector4()
+        {
+            return math.float4(Axis);
+        }
+
+        /// <summary>
+        /// Converts this instance to a full precision <see cref="Quaternion"/>.
+        /// </summary>
+        /// <returns>A <see cref="Quaternion"/> as the full precision value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Quaternion ToQuaternion()
+        {
+            return math.quaternion(Axis);
+        }
+
+        /// <summary>
+        /// Converts a full precision <see cref="Vector4"/> to half precision and updates the current instance.
+        /// </summary>
+        /// <param name="vector4">The <see cref="Vector4"/> to convert and update this instance with.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void UpdateFrom(ref Vector4 vector4)
+        {
+            Axis = math.half4(vector4);
+        }
+
+        /// <summary>
+        /// Converts a full precision <see cref="Vector4"/> to half precision and updates the current instance.
+        /// </summary>
+        /// <param name="quaternion">The <see cref="Quaternion"/> to convert and update this instance with.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void UpdateFrom(ref Quaternion quaternion)
+        {
+            Axis = math.half4(math.half(quaternion.x), math.half(quaternion.y), math.half(quaternion.z), math.half(quaternion.w));
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="vector4">The initial axial values (converted to half floats) when instantiated.</param>
+        public HalfVector4(Vector4 vector4)
+        {
+            Axis = default;
+            UpdateFrom(ref vector4);
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="x">The initial x axis (converted to half float) value when instantiated.</param>
+        /// <param name="y">The initial y axis (converted to half float) value when instantiated.</param>
+        /// <param name="z">The initial z axis (converted to half float) value when instantiated.</param>
+        /// <param name="w">The initial w axis (converted to half float) value when instantiated.</param>
+        public HalfVector4(float x, float y, float z, float w) : this(new Vector4(x, y, z, w))
+        {
+        }
+    }
+}

Components/HalfVector4.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 03c78136f41ff84499e2a6ac4a7dd7a5
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Components/Interpolator/BufferedLinearInterpolator.cs

@@ -248,6 +248,8 @@ namespace Unity.Netcode
                 return;
             }
 
+            // Part the of reason for disabling extrapolation is how we add and use measurements over time.
+            // TODO: Add detailed description of this area in Jira ticket
             if (sentTime > m_EndTimeConsumed || m_LifetimeConsumedCount == 0) // treat only if value is newer than the one being interpolated to right now
             {
                 m_LastBufferedItemReceived = new BufferedItem(newMeasurement, sentTime);
@@ -292,7 +294,9 @@ namespace Unity.Netcode
         /// <inheritdoc />
         protected override float InterpolateUnclamped(float start, float end, float time)
         {
-            return Mathf.LerpUnclamped(start, end, time);
+            // Disabling Extrapolation:
+            // TODO: Add Jira Ticket
+            return Mathf.Lerp(start, end, time);
         }
 
         /// <inheritdoc />
@@ -308,16 +312,79 @@ namespace Unity.Netcode
     /// </remarks>
     public class BufferedLinearInterpolatorQuaternion : BufferedLinearInterpolator<Quaternion>
     {
+        /// <summary>
+        /// Use <see cref="Quaternion.Slerp"/> when <see cref="true"/>.
+        /// Use <see cref="Quaternion.Lerp"/> when <see cref="false"/>
+        /// </summary>
+        /// <remarks>
+        /// When using half precision (due to the imprecision) using <see cref="Quaternion.Lerp"/> is
+        /// less processor intensive (i.e. precision is already "imprecise").
+        /// When using full precision (to maintain precision) using <see cref="Quaternion.Slerp"/> is
+        /// more processor intensive yet yields more precise results.
+        /// </remarks>
+        public bool IsSlerp;
+
         /// <inheritdoc />
         protected override Quaternion InterpolateUnclamped(Quaternion start, Quaternion end, float time)
         {
-            return Quaternion.SlerpUnclamped(start, end, time);
+            if (IsSlerp)
+            {
+                return Quaternion.Slerp(start, end, time);
+            }
+            else
+            {
+                return Quaternion.Lerp(start, end, time);
+            }
         }
 
         /// <inheritdoc />
         protected override Quaternion Interpolate(Quaternion start, Quaternion end, float time)
         {
-            return Quaternion.SlerpUnclamped(start, end, time);
+            if (IsSlerp)
+            {
+                return Quaternion.Slerp(start, end, time);
+            }
+            else
+            {
+                return Quaternion.Lerp(start, end, time);
+            }
+        }
+    }
+
+    /// <summary>
+    /// A <see cref="BufferedLinearInterpolator<T>"/> <see cref="Vector3"/> implementation.
+    /// </summary>
+    public class BufferedLinearInterpolatorVector3 : BufferedLinearInterpolator<Vector3>
+    {
+        /// <summary>
+        /// Use <see cref="Vector3.Slerp"/> when <see cref="true"/>.
+        /// Use <see cref="Vector3.Lerp"/> when <see cref="false"/>
+        /// </summary>
+        public bool IsSlerp;
+        /// <inheritdoc />
+        protected override Vector3 InterpolateUnclamped(Vector3 start, Vector3 end, float time)
+        {
+            if (IsSlerp)
+            {
+                return Vector3.Slerp(start, end, time);
+            }
+            else
+            {
+                return Vector3.Lerp(start, end, time);
+            }
+        }
+
+        /// <inheritdoc />
+        protected override Vector3 Interpolate(Vector3 start, Vector3 end, float time)
+        {
+            if (IsSlerp)
+            {
+                return Vector3.Slerp(start, end, time);
+            }
+            else
+            {
+                return Vector3.Lerp(start, end, time);
+            }
         }
     }
 }

Components/NetworkDeltaPosition.cs

@@ -0,0 +1,205 @@
+using System.Runtime.CompilerServices;
+using Unity.Mathematics;
+using UnityEngine;
+
+namespace Unity.Netcode.Components
+{
+    /// <summary>
+    /// Used to synchromnize delta position when half float precision is enabled
+    /// </summary>
+    public struct NetworkDeltaPosition : INetworkSerializable
+    {
+        internal const float MaxDeltaBeforeAdjustment = 64f;
+
+        /// <summary>
+        /// The HalfVector3 used to synchronize the delta in position
+        /// </summary>
+        public HalfVector3 HalfVector3;
+
+        internal Vector3 CurrentBasePosition;
+        internal Vector3 PrecisionLossDelta;
+        internal Vector3 HalfDeltaConvertedBack;
+        internal Vector3 PreviousPosition;
+        internal Vector3 DeltaPosition;
+        internal int NetworkTick;
+
+        /// <summary>
+        /// The serialization implementation of <see cref="INetworkSerializable"/>
+        /// </summary>
+        public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+            HalfVector3.NetworkSerialize(serializer);
+        }
+
+        /// <summary>
+        /// Gets the full precision value of Vector3 position while also potentially updating the current base position.
+        /// </summary>
+        /// <param name="networkTick">Use the current network tick value.</param>
+        /// <returns>The full position as a <see cref="Vector3"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 ToVector3(int networkTick)
+        {
+            // When synchronizing, it is possible to have a state update arrive
+            // for the same synchronization network tick.  Under this scenario,
+            // we only want to return the existing CurrentBasePosition + DeltaPosition
+            // values and not process the X, Y, or Z values.
+            // (See the constructors below)
+            if (networkTick == NetworkTick)
+            {
+                return CurrentBasePosition + DeltaPosition;
+            }
+            for (int i = 0; i < HalfVector3.Length; i++)
+            {
+                if (HalfVector3.AxisToSynchronize[i])
+                {
+                    DeltaPosition[i] = Mathf.HalfToFloat(HalfVector3.Axis[i].value);
+                    // If we exceed or are equal to the maximum delta value then we need to
+                    // apply the delta to the CurrentBasePosition value and reset the delta
+                    // position for the axis.
+                    if (Mathf.Abs(DeltaPosition[i]) >= MaxDeltaBeforeAdjustment)
+                    {
+                        CurrentBasePosition[i] += DeltaPosition[i];
+                        DeltaPosition[i] = 0.0f;
+                        HalfVector3.Axis[i] = half.zero;
+                    }
+                }
+            }
+            return CurrentBasePosition + DeltaPosition;
+        }
+
+        /// <summary>
+        /// Returns the current base position (excluding the delta position offset).
+        /// </summary>
+        /// <returns>The current base position as a <see cref="Vector3"/></returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 GetCurrentBasePosition()
+        {
+            return CurrentBasePosition;
+        }
+
+        /// <summary>
+        /// Returns the full position which includes the delta offset position.
+        /// </summary>
+        /// <returns>The full position as a <see cref="Vector3"/>.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 GetFullPosition()
+        {
+            return CurrentBasePosition + DeltaPosition;
+        }
+
+        /// <summary>
+        /// The half float vector3 version of the current delta position.
+        /// </summary>
+        /// <remarks>
+        /// Only applies to the authoritative side for <see cref="NetworkTransform"/> instances.
+        /// </remarks>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 GetConvertedDelta()
+        {
+            return HalfDeltaConvertedBack;
+        }
+
+        /// <summary>
+        /// The full precision current delta position.
+        /// </summary>
+        /// <remarks>
+        /// Authoritative: Will have no precision loss
+        /// Non-Authoritative: Has the current network tick's loss of precision.
+        /// Precision loss adjustments are one network tick behind on the
+        /// non-authoritative side.
+        /// </remarks>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public Vector3 GetDeltaPosition()
+        {
+            return DeltaPosition;
+        }
+
+        /// <summary>
+        /// Updates the position delta based off of the current base position.
+        /// </summary>
+        /// <param name="vector3">The full precision <see cref="Vector3"/> value to (converted to half floats) used to determine the delta offset positon.</param>
+        /// <param name="networkTick">Set the current network tick value when updating.</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void UpdateFrom(ref Vector3 vector3, int networkTick)
+        {
+            NetworkTick = networkTick;
+            DeltaPosition = (vector3 + PrecisionLossDelta) - CurrentBasePosition;
+            for (int i = 0; i < HalfVector3.Length; i++)
+            {
+                if (HalfVector3.AxisToSynchronize[i])
+                {
+                    HalfVector3.Axis[i] = math.half(DeltaPosition[i]);
+                    HalfDeltaConvertedBack[i] = Mathf.HalfToFloat(HalfVector3.Axis[i].value);
+                    PrecisionLossDelta[i] = DeltaPosition[i] - HalfDeltaConvertedBack[i];
+                    if (Mathf.Abs(HalfDeltaConvertedBack[i]) >= MaxDeltaBeforeAdjustment)
+                    {
+                        CurrentBasePosition[i] += HalfDeltaConvertedBack[i];
+                        HalfDeltaConvertedBack[i] = 0.0f;
+                        DeltaPosition[i] = 0.0f;
+                    }
+                }
+            }
+
+            for (int i = 0; i < HalfVector3.Length; i++)
+            {
+                if (HalfVector3.AxisToSynchronize[i])
+                {
+                    PreviousPosition[i] = vector3[i];
+                }
+            }
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="vector3">The initial axial values (converted to half floats) when instantiated.</param>
+        /// <param name="networkTick">Set the network tick value to the current network tick when instantiating.</param>
+        /// <param name="axisToSynchronize">The axis to be synchronized.</param>
+        public NetworkDeltaPosition(Vector3 vector3, int networkTick, bool3 axisToSynchronize)
+        {
+            NetworkTick = networkTick;
+            CurrentBasePosition = vector3;
+            PreviousPosition = vector3;
+            PrecisionLossDelta = Vector3.zero;
+            DeltaPosition = Vector3.zero;
+            HalfDeltaConvertedBack = Vector3.zero;
+            HalfVector3 = new HalfVector3(vector3, axisToSynchronize);
+            UpdateFrom(ref vector3, networkTick);
+        }
+
+        /// <summary>
+        /// Constructor that defaults to all axis being synchronized.
+        /// </summary>
+        /// <param name="vector3">The initial axial values (converted to half floats) when instantiated.</param>
+        /// <param name="networkTick">Set the network tick value to the current network tick when instantiating.</param>
+        public NetworkDeltaPosition(Vector3 vector3, int networkTick) : this(vector3, networkTick, math.bool3(true))
+        {
+
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="x">The initial x axis (converted to half float) value when instantiated.</param>
+        /// <param name="y">The initial y axis (converted to half float) value when instantiated.</param>
+        /// <param name="z">The initial z axis (converted to half float) value when instantiated.</param>
+        /// <param name="networkTick">Set the network tick value to the current network tick when instantiating.</param>
+        /// <param name="axisToSynchronize">The axis to be synchronized.</param>
+        public NetworkDeltaPosition(float x, float y, float z, int networkTick, bool3 axisToSynchronize) :
+            this(new Vector3(x, y, z), networkTick, axisToSynchronize)
+        {
+        }
+
+        /// <summary>
+        /// Constructor
+        /// </summary>
+        /// <param name="x">The initial x axis (converted to half float) value when instantiated.</param>
+        /// <param name="y">The initial y axis (converted to half float) value when instantiated.</param>
+        /// <param name="z">The initial z axis (converted to half float) value when instantiated.</param>
+        /// <param name="networkTick">Set the network tick value to the current network tick when instantiating.</param>
+        public NetworkDeltaPosition(float x, float y, float z, int networkTick) :
+            this(new Vector3(x, y, z), networkTick, math.bool3(true))
+        {
+        }
+    }
+}

Components/NetworkDeltaPosition.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e45e6886578116f4c92fa0fe0d77fb85
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Components/NetworkRigidbody.cs

@@ -9,6 +9,7 @@ namespace Unity.Netcode.Components
     /// </summary>
     [RequireComponent(typeof(Rigidbody))]
     [RequireComponent(typeof(NetworkTransform))]
+    [AddComponentMenu("Netcode/Network Rigidbody")]
     public class NetworkRigidbody : NetworkBehaviour
     {
         /// <summary>

Components/NetworkRigidbody2D.cs

@@ -9,6 +9,7 @@ namespace Unity.Netcode.Components
     /// </summary>
     [RequireComponent(typeof(Rigidbody2D))]
     [RequireComponent(typeof(NetworkTransform))]
+    [AddComponentMenu("Netcode/Network Rigidbody 2D")]
     public class NetworkRigidbody2D : NetworkBehaviour
     {
         private Rigidbody2D m_Rigidbody;

Components/QuaternionCompressor.cs

@@ -0,0 +1,123 @@
+using System.Runtime.CompilerServices;
+using UnityEngine;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// A Smallest Three Quaternion Compressor Implementation
+    /// </summary>
+    /// <remarks>
+    /// Explanation of why "The smallest three":
+    /// Since a normalized Quaternion's unit value is 1.0f:
+    /// x*x + y*y + z*z + w*w = M*M (where M is the magnitude of the vector)
+    /// If w was the largest value and the quaternion is normalized:
+    /// M = 1.0f (which M * M would still yield 1.0f)
+    /// w*w = M*M - (x*x + y*y + z*z) or Mathf.Sqrt(1.0f - (x*x + y*y + z*z))
+    /// w = Math.Sqrt(1.0f - (x*x + y*y + z*z))
+    /// Using the largest the number avoids potential loss of precision in the smallest three values.
+    /// </remarks>
+    public static class QuaternionCompressor
+    {
+        private const ushort k_PrecisionMask = (1 << 9) - 1;
+
+        // Square root of 2 over 2 (Mathf.Sqrt(2.0f) / 2.0f == 1.0f / Mathf.Sqrt(2.0f))
+        // This provides encoding the smallest three components into a (+/-) Mathf.Sqrt(2.0f) / 2.0f range
+        private const float k_SqrtTwoOverTwoEncoding = 0.70710678118654752440084436210485f;
+
+        // We can further improve the encoding compression by dividing k_SqrtTwoOverTwo into 1.0f and multiplying that
+        // by the precision mask (minor reduction of runtime calculations)
+        private const float k_CompressionEcodingMask = (1.0f / k_SqrtTwoOverTwoEncoding) * k_PrecisionMask;
+
+        // Used to shift the negative bit to the 10th bit position when compressing and encoding
+        private const ushort k_ShiftNegativeBit = 9;
+
+        // We can do the same for our decoding and decompression by dividing k_PrecisionMask into 1.0 and multiplying
+        // that by k_SqrtTwoOverTwo (minor reduction of runtime calculations)
+        private const float k_DcompressionDecodingMask = (1.0f / k_PrecisionMask) * k_SqrtTwoOverTwoEncoding;
+
+        // The sign bit position (10th bit) used when decompressing and decoding
+        private const ushort k_NegShortBit = 0x200;
+
+        // Negative bit set values
+        private const ushort k_True = 1;
+        private const ushort k_False = 0;
+
+        // Used to store the absolute value of the 4 quaternion elements
+        private static Quaternion s_QuatAbsValues = Quaternion.identity;
+
+        /// <summary>
+        /// Compresses a Quaternion into an unsigned integer
+        /// </summary>
+        /// <param name="quaternion">the <see cref="Quaternion"/> to be compressed</param>
+        /// <returns>the <see cref="Quaternion"/> compressed as an unsigned integer</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint CompressQuaternion(ref Quaternion quaternion)
+        {
+            // Store off the absolute value for each Quaternion element
+            s_QuatAbsValues[0] = Mathf.Abs(quaternion[0]);
+            s_QuatAbsValues[1] = Mathf.Abs(quaternion[1]);
+            s_QuatAbsValues[2] = Mathf.Abs(quaternion[2]);
+            s_QuatAbsValues[3] = Mathf.Abs(quaternion[3]);
+
+            // Get the largest element value of the quaternion to know what the remaining "Smallest Three" values are
+            var quatMax = Mathf.Max(s_QuatAbsValues[0], s_QuatAbsValues[1], s_QuatAbsValues[2], s_QuatAbsValues[3]);
+
+            // Find the index of the largest element so we can skip that element while compressing and decompressing
+            var indexToSkip = (ushort)(s_QuatAbsValues[0] == quatMax ? 0 : s_QuatAbsValues[1] == quatMax ? 1 : s_QuatAbsValues[2] == quatMax ? 2 : 3);
+
+            // Get the sign of the largest element which is all that is needed when calculating the sum of squares of a normalized quaternion.
+
+            var quatMaxSign = (quaternion[indexToSkip] < 0 ? k_True : k_False);
+
+            // Start with the index to skip which will be shifted to the highest two bits
+            var compressed = (uint)indexToSkip;
+
+            // Step 1: Start with the first element
+            var currentIndex = 0;
+
+            // Step 2: If we are on the index to skip preserve the current compressed value, otherwise proceed to step 3 and 4
+            // Step 3: Get the sign of the element we are processing. If it is the not the same as the largest value's sign bit then we set the bit
+            // Step 4: Get the compressed and encoded value by multiplying the absolute value of the current element by k_CompressionEcodingMask and round that result up
+            compressed = currentIndex != indexToSkip ? (compressed << 10) | (uint)((quaternion[currentIndex] < 0 ? k_True : k_False) != quatMaxSign ? k_True : k_False) << k_ShiftNegativeBit | (ushort)Mathf.Round(k_CompressionEcodingMask * s_QuatAbsValues[currentIndex]) : compressed;
+            currentIndex++;
+            // Repeat the last 3 steps for the remaining elements
+            compressed = currentIndex != indexToSkip ? (compressed << 10) | (uint)((quaternion[currentIndex] < 0 ? k_True : k_False) != quatMaxSign ? k_True : k_False) << k_ShiftNegativeBit | (ushort)Mathf.Round(k_CompressionEcodingMask * s_QuatAbsValues[currentIndex]) : compressed;
+            currentIndex++;
+            compressed = currentIndex != indexToSkip ? (compressed << 10) | (uint)((quaternion[currentIndex] < 0 ? k_True : k_False) != quatMaxSign ? k_True : k_False) << k_ShiftNegativeBit | (ushort)Mathf.Round(k_CompressionEcodingMask * s_QuatAbsValues[currentIndex]) : compressed;
+            currentIndex++;
+            compressed = currentIndex != indexToSkip ? (compressed << 10) | (uint)((quaternion[currentIndex] < 0 ? k_True : k_False) != quatMaxSign ? k_True : k_False) << k_ShiftNegativeBit | (ushort)Mathf.Round(k_CompressionEcodingMask * s_QuatAbsValues[currentIndex]) : compressed;
+
+            // Return the compress quaternion
+            return compressed;
+        }
+
+        /// <summary>
+        /// Decompress a compressed quaternion
+        /// </summary>
+        /// <param name="quaternion">quaternion to store the decompressed values within</param>
+        /// <param name="compressed">the compressed quaternion</param>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void DecompressQuaternion(ref Quaternion quaternion, uint compressed)
+        {
+            // Get the last two bits for the index to skip (0-3)
+            var indexToSkip = (int)(compressed >> 30);
+
+            // Reverse out the values while skipping over the largest value index
+            var sumOfSquaredMagnitudes = 0.0f;
+            for (int i = 3; i >= 0; --i)
+            {
+                if (i == indexToSkip)
+                {
+                    continue;
+                }
+                // Check the negative bit and multiply that result with the decompressed and decoded value
+                quaternion[i] = ((compressed & k_NegShortBit) > 0 ? -1.0f : 1.0f) * ((compressed & k_PrecisionMask) * k_DcompressionDecodingMask);
+                sumOfSquaredMagnitudes += quaternion[i] * quaternion[i];
+                compressed = compressed >> 10;
+            }
+            // Since a normalized quaternion's magnitude is 1.0f, we subtract the sum of the squared smallest three from the unit value and take
+            // the square root of the difference to find the final largest value
+            quaternion[indexToSkip] = Mathf.Sqrt(1.0f - sumOfSquaredMagnitudes);
+        }
+    }
+}

Components/QuaternionCompressor.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: bb9d8b98d3c8bca469c8ee152353336f
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Components/com.unity.netcode.components.asmdef

@@ -3,7 +3,8 @@
     "rootNamespace": "Unity.Netcode.Components",
     "references": [
         "Unity.Netcode.Runtime",
-        "Unity.Collections"
+        "Unity.Collections",
+        "Unity.Mathematics"
     ],
     "allowUnsafeCode": true,
     "versionDefines": [

Editor/AssemblyInfo.cs

@@ -1,3 +1,7 @@
 using System.Runtime.CompilerServices;
 
+#if UNITY_INCLUDE_TESTS
+#if UNITY_EDITOR
 [assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+#endif // UNITY_EDITOR
+#endif // UNITY_INCLUDE_TESTS

Editor/CodeGen/CodeGenHelpers.cs

@@ -15,6 +15,10 @@ namespace Unity.Netcode.Editor.CodeGen
 {
     internal static class CodeGenHelpers
     {
+        public const string DotnetModuleName = "netstandard.dll";
+        public const string UnityModuleName = "UnityEngine.CoreModule.dll";
+        public const string NetcodeModuleName = "Unity.Netcode.Runtime.dll";
+
         public const string RuntimeAssemblyName = "Unity.Netcode.Runtime";
 
         public static readonly string NetworkBehaviour_FullName = typeof(NetworkBehaviour).FullName;
@@ -119,6 +123,19 @@ namespace Unity.Netcode.Editor.CodeGen
             try
             {
                 var typeDef = typeReference.Resolve();
+                // Note: this won't catch generics correctly.
+                //
+                //     class Foo<T>: IInterface<T> {}
+                //     class Bar: Foo<int> {}
+                //
+                // Bar.HasInterface(IInterface<int>) -> returns false even though it should be true.
+                //
+                // This can be fixed (see GetAllFieldsAndResolveGenerics() in NetworkBehaviourILPP to understand how)
+                // but right now we don't need that to work so it's left alone to reduce complexity
+                if (typeDef.BaseType.HasInterface(interfaceTypeFullName))
+                {
+                    return true;
+                }
                 var typeFaces = typeDef.Interfaces;
                 return typeFaces.Any(iface => iface.InterfaceType.FullName == interfaceTypeFullName);
             }
@@ -380,5 +397,74 @@ namespace Unity.Netcode.Editor.CodeGen
 
             return assemblyDefinition;
         }
+
+        private static void SearchForBaseModulesRecursive(AssemblyDefinition assemblyDefinition, PostProcessorAssemblyResolver assemblyResolver, ref ModuleDefinition unityModule, ref ModuleDefinition netcodeModule, HashSet<string> visited)
+        {
+
+            foreach (var module in assemblyDefinition.Modules)
+            {
+                if (module == null)
+                {
+                    continue;
+                }
+
+                if (unityModule != null && netcodeModule != null)
+                {
+                    return;
+                }
+
+                if (unityModule == null && module.Name == UnityModuleName)
+                {
+                    unityModule = module;
+                    continue;
+                }
+
+                if (netcodeModule == null && module.Name == NetcodeModuleName)
+                {
+                    netcodeModule = module;
+                    continue;
+                }
+            }
+            if (unityModule != null && netcodeModule != null)
+            {
+                return;
+            }
+
+            foreach (var assemblyNameReference in assemblyDefinition.MainModule.AssemblyReferences)
+            {
+                if (assemblyNameReference == null)
+                {
+                    continue;
+                }
+                if (visited.Contains(assemblyNameReference.Name))
+                {
+                    continue;
+                }
+
+                visited.Add(assemblyNameReference.Name);
+
+                var assembly = assemblyResolver.Resolve(assemblyNameReference);
+                if (assembly == null)
+                {
+                    continue;
+                }
+                SearchForBaseModulesRecursive(assembly, assemblyResolver, ref unityModule, ref netcodeModule, visited);
+
+                if (unityModule != null && netcodeModule != null)
+                {
+                    return;
+                }
+            }
+        }
+
+        public static (ModuleDefinition UnityModule, ModuleDefinition NetcodeModule) FindBaseModules(AssemblyDefinition assemblyDefinition, PostProcessorAssemblyResolver assemblyResolver)
+        {
+            ModuleDefinition unityModule = null;
+            ModuleDefinition netcodeModule = null;
+            var visited = new HashSet<string>();
+            SearchForBaseModulesRecursive(assemblyDefinition, assemblyResolver, ref unityModule, ref netcodeModule, visited);
+
+            return (unityModule, netcodeModule);
+        }
     }
 }

Editor/CodeGen/INetworkMessageILPP.cs

@@ -1,8 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using System.Collections.Generic;
-using System.Reflection;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 using Mono.Cecil.Rocks;
@@ -17,9 +16,7 @@ namespace Unity.Netcode.Editor.CodeGen
     {
         public override ILPPInterface GetInstance() => this;
 
-        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName;
-            compiledAssembly.Name == CodeGenHelpers.RuntimeAssemblyName ||
-            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
@@ -33,13 +30,22 @@ namespace Unity.Netcode.Editor.CodeGen
             m_Diagnostics.Clear();
 
             // read
-            var assemblyDefinition = CodeGenHelpers.AssemblyDefinitionFor(compiledAssembly, out var resolver);
+            var assemblyDefinition = CodeGenHelpers.AssemblyDefinitionFor(compiledAssembly, out m_AssemblyResolver);
             if (assemblyDefinition == null)
             {
                 m_Diagnostics.AddError($"Cannot read assembly definition: {compiledAssembly.Name}");
                 return null;
             }
 
+            // modules
+            (_, m_NetcodeModule) = CodeGenHelpers.FindBaseModules(assemblyDefinition, m_AssemblyResolver);
+
+            if (m_NetcodeModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Netcode module: {CodeGenHelpers.NetcodeModuleName}");
+                return null;
+            }
+
             // process
             var mainModule = assemblyDefinition.MainModule;
             if (mainModule != null)
@@ -61,7 +67,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     }
                     catch (Exception e)
                     {
-                        m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                        m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                     }
                 }
                 else
@@ -92,77 +98,136 @@ namespace Unity.Netcode.Editor.CodeGen
             return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
         }
 
+        private ModuleDefinition m_NetcodeModule;
+        private PostProcessorAssemblyResolver m_AssemblyResolver;
 
         private MethodReference m_MessagingSystem_ReceiveMessage_MethodRef;
+        private MethodReference m_MessagingSystem_CreateMessageAndGetVersion_MethodRef;
         private TypeReference m_MessagingSystem_MessageWithHandler_TypeRef;
         private MethodReference m_MessagingSystem_MessageHandler_Constructor_TypeRef;
+        private MethodReference m_MessagingSystem_VersionGetter_Constructor_TypeRef;
         private FieldReference m_ILPPMessageProvider___network_message_types_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_MessageType_FieldRef;
         private FieldReference m_MessagingSystem_MessageWithHandler_Handler_FieldRef;
+        private FieldReference m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef;
         private MethodReference m_Type_GetTypeFromHandle_MethodRef;
         private MethodReference m_List_Add_MethodRef;
 
         private const string k_ReceiveMessageName = nameof(MessagingSystem.ReceiveMessage);
+        private const string k_CreateMessageAndGetVersionName = nameof(MessagingSystem.CreateMessageAndGetVersion);
 
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
-            m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(typeof(MessagingSystem.MessageHandler).GetConstructors()[0]);
+            // Different environments seem to have different situations...
+            // Some have these definitions in netstandard.dll...
+            // some seem to have them elsewhere...
+            // Since they're standard .net classes they're not going to cause
+            // the same issues as referencing other assemblies, in theory, since
+            // the definitions should be standard and consistent across platforms
+            // (i.e., there's no #if UNITY_EDITOR in them that could create
+            // invalid IL code)
+            TypeDefinition typeTypeDef = moduleDefinition.ImportReference(typeof(Type)).Resolve();
+            TypeDefinition listTypeDef = moduleDefinition.ImportReference(typeof(List<>)).Resolve();
 
-            var messageWithHandlerType = typeof(MessagingSystem.MessageWithHandler);
+            TypeDefinition messageHandlerTypeDef = null;
-            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerType);
+            TypeDefinition versionGetterTypeDef = null;
-            foreach (var fieldInfo in messageWithHandlerType.GetFields())
+            TypeDefinition messageWithHandlerTypeDef = null;
+            TypeDefinition ilppMessageProviderTypeDef = null;
+            TypeDefinition messagingSystemTypeDef = null;
+            foreach (var netcodeTypeDef in m_NetcodeModule.GetAllTypes())
             {
-                switch (fieldInfo.Name)
+                if (messageHandlerTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.MessageHandler))
+                {
+                    messageHandlerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (versionGetterTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.VersionGetter))
+                {
+                    versionGetterTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (messageWithHandlerTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem.MessageWithHandler))
+                {
+                    messageWithHandlerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (ilppMessageProviderTypeDef == null && netcodeTypeDef.Name == nameof(ILPPMessageProvider))
+                {
+                    ilppMessageProviderTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (messagingSystemTypeDef == null && netcodeTypeDef.Name == nameof(MessagingSystem))
+                {
+                    messagingSystemTypeDef = netcodeTypeDef;
+                    continue;
+                }
+            }
+
+            m_MessagingSystem_MessageHandler_Constructor_TypeRef = moduleDefinition.ImportReference(messageHandlerTypeDef.GetConstructors().First());
+            m_MessagingSystem_VersionGetter_Constructor_TypeRef = moduleDefinition.ImportReference(versionGetterTypeDef.GetConstructors().First());
+
+            m_MessagingSystem_MessageWithHandler_TypeRef = moduleDefinition.ImportReference(messageWithHandlerTypeDef);
+            foreach (var fieldDef in messageWithHandlerTypeDef.Fields)
+            {
+                switch (fieldDef.Name)
                 {
                     case nameof(MessagingSystem.MessageWithHandler.MessageType):
-                        m_MessagingSystem_MessageWithHandler_MessageType_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_MessagingSystem_MessageWithHandler_MessageType_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case nameof(MessagingSystem.MessageWithHandler.Handler):
-                        m_MessagingSystem_MessageWithHandler_Handler_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_MessagingSystem_MessageWithHandler_Handler_FieldRef = moduleDefinition.ImportReference(fieldDef);
+                        break;
+                    case nameof(MessagingSystem.MessageWithHandler.GetVersion):
+                        m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var typeType = typeof(Type);
+            foreach (var methodDef in typeTypeDef.Methods)
-            foreach (var methodInfo in typeType.GetMethods())
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case nameof(Type.GetTypeFromHandle):
-                        m_Type_GetTypeFromHandle_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_Type_GetTypeFromHandle_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
 
-            var ilppMessageProviderType = typeof(ILPPMessageProvider);
+            foreach (var fieldDef in ilppMessageProviderTypeDef.Fields)
-            foreach (var fieldInfo in ilppMessageProviderType.GetFields(BindingFlags.Static | BindingFlags.NonPublic))
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case nameof(ILPPMessageProvider.__network_message_types):
-                        m_ILPPMessageProvider___network_message_types_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_ILPPMessageProvider___network_message_types_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var listType = typeof(List<MessagingSystem.MessageWithHandler>);
+            foreach (var methodDef in listTypeDef.Methods)
-            foreach (var methodInfo in listType.GetMethods())
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
-                    case nameof(List<MessagingSystem.MessageWithHandler>.Add):
+                    case "Add":
-                        m_List_Add_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_List_Add_MethodRef = methodDef;
+                        m_List_Add_MethodRef.DeclaringType = listTypeDef.MakeGenericInstanceType(messageWithHandlerTypeDef);
+                        m_List_Add_MethodRef = moduleDefinition.ImportReference(m_List_Add_MethodRef);
                         break;
                 }
             }
 
-            var messagingSystemType = typeof(MessagingSystem);
+            foreach (var methodDef in messagingSystemTypeDef.Methods)
-            foreach (var methodInfo in messagingSystemType.GetMethods(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case k_ReceiveMessageName:
-                        m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_MessagingSystem_ReceiveMessage_MethodRef = moduleDefinition.ImportReference(methodDef);
+                        break;
+                    case k_CreateMessageAndGetVersionName:
+                        m_MessagingSystem_CreateMessageAndGetVersion_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
@@ -189,7 +254,7 @@ namespace Unity.Netcode.Editor.CodeGen
             return staticCtorMethodDef;
         }
 
-        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod)
+        private void CreateInstructionsToRegisterType(ILProcessor processor, List<Instruction> instructions, TypeReference type, MethodReference receiveMethod, MethodReference versionMethod)
         {
             // MessagingSystem.__network_message_types.Add(new MessagingSystem.MessageWithHandler{MessageType=typeof(type), Handler=type.Receive});
             processor.Body.Variables.Add(new VariableDefinition(m_MessagingSystem_MessageWithHandler_TypeRef));
@@ -205,7 +270,7 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Call, m_Type_GetTypeFromHandle_MethodRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_MessageType_FieldRef));
 
-            // tmp.Handler = type.Receive
+            // tmp.Handler = MessageHandler.ReceveMessage<type>
             instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Ldnull));
 
@@ -213,15 +278,22 @@ namespace Unity.Netcode.Editor.CodeGen
             instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_MessageHandler_Constructor_TypeRef));
             instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_Handler_FieldRef));
 
+
+            // tmp.GetVersion = MessageHandler.CreateMessageAndGetVersion<type>
+            instructions.Add(processor.Create(OpCodes.Ldloca, messageWithHandlerLocIdx));
+            instructions.Add(processor.Create(OpCodes.Ldnull));
+
+            instructions.Add(processor.Create(OpCodes.Ldftn, versionMethod));
+            instructions.Add(processor.Create(OpCodes.Newobj, m_MessagingSystem_VersionGetter_Constructor_TypeRef));
+            instructions.Add(processor.Create(OpCodes.Stfld, m_MessagingSystem_MessageWithHandler_GetVersion_FieldRef));
+
             // ILPPMessageProvider.__network_message_types.Add(tmp);
             instructions.Add(processor.Create(OpCodes.Ldloc, messageWithHandlerLocIdx));
             instructions.Add(processor.Create(OpCodes.Callvirt, m_List_Add_MethodRef));
         }
 
-        // Creates a static module constructor (which is executed when the module is loaded) that registers all the
+        // Creates a static module constructor (which is executed when the module is loaded) that registers all the message types in the assembly with MessagingSystem.
-        // message types in the assembly with MessagingSystem.
+        // This is the same behavior as annotating a static method with [ModuleInitializer] in standardized C# (that attribute doesn't exist in Unity, but the static module constructor still works).
-        // This is the same behavior as annotating a static method with [ModuleInitializer] in standardized
-        // C# (that attribute doesn't exist in Unity, but the static module constructor still works)
         // https://docs.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.moduleinitializerattribute?view=net-5.0
         // https://web.archive.org/web/20100212140402/http://blogs.msdn.com/junfeng/archive/2005/11/19/494914.aspx
         private void CreateModuleInitializer(AssemblyDefinition assembly, List<TypeDefinition> networkMessageTypes)
@@ -240,7 +312,9 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         var receiveMethod = new GenericInstanceMethod(m_MessagingSystem_ReceiveMessage_MethodRef);
                         receiveMethod.GenericArguments.Add(type);
-                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod);
+                        var versionMethod = new GenericInstanceMethod(m_MessagingSystem_CreateMessageAndGetVersion_MethodRef);
+                        versionMethod.GenericArguments.Add(type);
+                        CreateInstructionsToRegisterType(processor, instructions, type, receiveMethod, versionMethod);
                     }
 
                     instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));

Editor/CodeGen/INetworkSerializableILPP.cs

@@ -1,7 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using System.Collections.Generic;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
 using Unity.CompilationPipeline.Common.Diagnostics;
@@ -10,7 +10,6 @@ using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostPr
 
 namespace Unity.Netcode.Editor.CodeGen
 {
-
     internal sealed class INetworkSerializableILPP : ILPPInterface
     {
         public override ILPPInterface GetInstance() => this;
@@ -92,7 +91,7 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
                 catch (Exception e)
                 {
-                    m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                    m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                 }
             }
             else

Editor/CodeGen/NetworkBehaviourILPP.cs

@@ -1,8 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
-using System.Collections.Generic;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using Mono.Cecil;
 using Mono.Cecil.Cil;
@@ -10,9 +9,9 @@ using Mono.Cecil.Rocks;
 using Unity.CompilationPipeline.Common.Diagnostics;
 using Unity.CompilationPipeline.Common.ILPostProcessing;
 using UnityEngine;
+using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostProcessor;
 using MethodAttributes = Mono.Cecil.MethodAttributes;
 using ParameterAttributes = Mono.Cecil.ParameterAttributes;
-using ILPPInterface = Unity.CompilationPipeline.Common.ILPostProcessing.ILPostProcessor;
 
 namespace Unity.Netcode.Editor.CodeGen
 {
@@ -23,8 +22,7 @@ namespace Unity.Netcode.Editor.CodeGen
 
         public override ILPPInterface GetInstance() => this;
 
-        public override bool WillProcess(ICompiledAssembly compiledAssembly) =>
+        public override bool WillProcess(ICompiledAssembly compiledAssembly) => compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
-            compiledAssembly.References.Any(filePath => Path.GetFileNameWithoutExtension(filePath) == CodeGenHelpers.RuntimeAssemblyName);
 
         private readonly List<DiagnosticMessage> m_Diagnostics = new List<DiagnosticMessage>();
 
@@ -35,7 +33,6 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
-
             m_Diagnostics.Clear();
 
             // read
@@ -46,11 +43,27 @@ namespace Unity.Netcode.Editor.CodeGen
                 return null;
             }
 
+            // modules
+            (m_UnityModule, m_NetcodeModule) = CodeGenHelpers.FindBaseModules(assemblyDefinition, m_AssemblyResolver);
+
+            if (m_UnityModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Unity module: {CodeGenHelpers.UnityModuleName}");
+                return null;
+            }
+
+            if (m_NetcodeModule == null)
+            {
+                m_Diagnostics.AddError($"Cannot find Netcode module: {CodeGenHelpers.NetcodeModuleName}");
+                return null;
+            }
+
             // process
             var mainModule = assemblyDefinition.MainModule;
             if (mainModule != null)
             {
                 m_MainModule = mainModule;
+
                 if (ImportReferences(mainModule))
                 {
                     // process `NetworkBehaviour` types
@@ -60,10 +73,12 @@ namespace Unity.Netcode.Editor.CodeGen
                             .Where(t => t.IsSubclassOf(CodeGenHelpers.NetworkBehaviour_FullName))
                             .ToList()
                             .ForEach(b => ProcessNetworkBehaviour(b, compiledAssembly.Defines));
+
+                        CreateNetworkVariableTypeInitializers(assemblyDefinition);
                     }
                     catch (Exception e)
                     {
-                        m_Diagnostics.AddError((e.ToString() + e.StackTrace.ToString()).Replace("\n", "|").Replace("\r", "|"));
+                        m_Diagnostics.AddError((e.ToString() + e.StackTrace).Replace("\n", "|").Replace("\r", "|"));
                     }
                 }
                 else
@@ -92,7 +107,135 @@ namespace Unity.Netcode.Editor.CodeGen
             return new ILPostProcessResult(new InMemoryAssembly(pe.ToArray(), pdb.ToArray()), m_Diagnostics);
         }
 
+        private MethodDefinition GetOrCreateStaticConstructor(TypeDefinition typeDefinition)
+        {
+            var staticCtorMethodDef = typeDefinition.GetStaticConstructor();
+            if (staticCtorMethodDef == null)
+            {
+                staticCtorMethodDef = new MethodDefinition(
+                    ".cctor", // Static Constructor (constant-constructor)
+                    MethodAttributes.HideBySig |
+                    MethodAttributes.SpecialName |
+                    MethodAttributes.RTSpecialName |
+                    MethodAttributes.Static,
+                    typeDefinition.Module.TypeSystem.Void);
+                staticCtorMethodDef.Body.Instructions.Add(Instruction.Create(OpCodes.Ret));
+                typeDefinition.Methods.Add(staticCtorMethodDef);
+            }
+
+            return staticCtorMethodDef;
+        }
+
+        private bool IsMemcpyableType(TypeReference type)
+        {
+            foreach (var supportedType in BaseSupportedTypes)
+            {
+                if (type.FullName == supportedType.FullName)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private bool IsSpecialCaseType(TypeReference type)
+        {
+            foreach (var supportedType in SpecialCaseTypes)
+            {
+                if (type.FullName == supportedType.FullName)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private void CreateNetworkVariableTypeInitializers(AssemblyDefinition assembly)
+        {
+            foreach (var typeDefinition in assembly.MainModule.Types)
+            {
+                if (typeDefinition.FullName == "<Module>")
+                {
+                    var staticCtorMethodDef = GetOrCreateStaticConstructor(typeDefinition);
+
+                    var processor = staticCtorMethodDef.Body.GetILProcessor();
+
+                    var instructions = new List<Instruction>();
+
+                    foreach (var type in m_WrappedNetworkVariableTypes)
+                    {
+                        if (IsSpecialCaseType(type))
+                        {
+                            continue;
+                        }
+
+                        // If a serializable type isn't found, FallbackSerializer will be used automatically, which will
+                        // call into UserNetworkVariableSerialization, giving the user a chance to define their own serializaiton
+                        // for types that aren't in our official supported types list.
+                        GenericInstanceMethod serializeMethod = null;
+                        GenericInstanceMethod equalityMethod;
+
+                        if (type.IsValueType)
+                        {
+                            if (type.HasInterface(typeof(INetworkSerializeByMemcpy).FullName) || type.Resolve().IsEnum || IsMemcpyableType(type))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef);
+                            }
+                            else if (type.HasInterface(typeof(INetworkSerializable).FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef);
+                            }
+                            else if (type.HasInterface(CodeGenHelpers.IUTF8Bytes_FullName) && type.HasInterface(k_INativeListBool_FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef);
+                            }
+
+                            if (type.HasInterface(typeof(IEquatable<>).FullName + "<" + type.FullName + ">"))
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef);
+                            }
+                            else
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef);
+                            }
+                        }
+                        else
+                        {
+                            if (type.HasInterface(typeof(INetworkSerializable).FullName))
+                            {
+                                serializeMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef);
+                            }
+
+                            if (type.HasInterface(typeof(IEquatable<>).FullName + "<" + type.FullName + ">"))
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef);
+                            }
+                            else
+                            {
+                                equalityMethod = new GenericInstanceMethod(m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef);
+                            }
+                        }
+
+                        if (serializeMethod != null)
+                        {
+                            serializeMethod.GenericArguments.Add(type);
+                            instructions.Add(processor.Create(OpCodes.Call, m_MainModule.ImportReference(serializeMethod)));
+                        }
+                        equalityMethod.GenericArguments.Add(type);
+                        instructions.Add(processor.Create(OpCodes.Call, m_MainModule.ImportReference(equalityMethod)));
+                    }
+
+                    instructions.ForEach(instruction => processor.Body.Instructions.Insert(processor.Body.Instructions.Count - 1, instruction));
+                    break;
+                }
+            }
+        }
+
         private ModuleDefinition m_MainModule;
+        private ModuleDefinition m_UnityModule;
+        private ModuleDefinition m_NetcodeModule;
         private PostProcessorAssemblyResolver m_AssemblyResolver;
 
         private MethodReference m_Debug_LogError_MethodRef;
@@ -123,14 +266,76 @@ namespace Unity.Netcode.Editor.CodeGen
         private FieldReference m_ServerRpcParams_Receive_FieldRef;
         private FieldReference m_ServerRpcParams_Receive_SenderClientId_FieldRef;
         private TypeReference m_ClientRpcParams_TypeRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef;
+        private MethodReference m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef;
+
+        private MethodReference m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+        private MethodReference m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+        private MethodReference m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
 
         private TypeReference m_FastBufferWriter_TypeRef;
-        private Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
+        private readonly Dictionary<string, MethodReference> m_FastBufferWriter_WriteValue_MethodRefs = new Dictionary<string, MethodReference>();
-        private List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
+        private readonly List<MethodReference> m_FastBufferWriter_ExtensionMethodRefs = new List<MethodReference>();
 
         private TypeReference m_FastBufferReader_TypeRef;
-        private Dictionary<string, MethodReference> m_FastBufferReader_ReadValue_MethodRefs = new Dictionary<string, MethodReference>();
+        private readonly Dictionary<string, MethodReference> m_FastBufferReader_ReadValue_MethodRefs = new Dictionary<string, MethodReference>();
-        private List<MethodReference> m_FastBufferReader_ExtensionMethodRefs = new List<MethodReference>();
+        private readonly List<MethodReference> m_FastBufferReader_ExtensionMethodRefs = new List<MethodReference>();
+
+        private HashSet<TypeReference> m_WrappedNetworkVariableTypes = new HashSet<TypeReference>();
+
+        internal static readonly Type[] BaseSupportedTypes = new[]
+        {
+            typeof(bool),
+            typeof(byte),
+            typeof(sbyte),
+            typeof(char),
+            typeof(decimal),
+            typeof(double),
+            typeof(float),
+            // the following types have special handling
+            /*typeof(int),
+            typeof(uint),
+            typeof(long),
+            typeof(ulong),
+            typeof(short),
+            typeof(ushort),*/
+            typeof(Vector2),
+            typeof(Vector3),
+            typeof(Vector2Int),
+            typeof(Vector3Int),
+            typeof(Vector4),
+            typeof(Quaternion),
+            typeof(Color),
+            typeof(Color32),
+            typeof(Ray),
+            typeof(Ray2D)
+        };
+        internal static readonly Type[] SpecialCaseTypes = new[]
+        {
+            // the following types have special handling
+            typeof(int),
+            typeof(uint),
+            typeof(long),
+            typeof(ulong),
+            typeof(short),
+            typeof(ushort),
+        };
 
         private const string k_Debug_LogError = nameof(Debug.LogError);
         private const string k_NetworkManager_LocalClientId = nameof(NetworkManager.LocalClientId);
@@ -157,160 +362,257 @@ namespace Unity.Netcode.Editor.CodeGen
         private const string k_ServerRpcParams_Receive = nameof(ServerRpcParams.Receive);
         private const string k_ServerRpcReceiveParams_SenderClientId = nameof(ServerRpcReceiveParams.SenderClientId);
 
+        // CodeGen cannot reference the collections assembly to do a typeof() on it due to a bug that causes that to crash.
+        private const string k_INativeListBool_FullName = "Unity.Collections.INativeList`1<System.Byte>";
+
         private bool ImportReferences(ModuleDefinition moduleDefinition)
         {
-            var debugType = typeof(Debug);
+            TypeDefinition debugTypeDef = null;
-            foreach (var methodInfo in debugType.GetMethods())
+            foreach (var unityTypeDef in m_UnityModule.GetAllTypes())
             {
-                switch (methodInfo.Name)
+                if (debugTypeDef == null && unityTypeDef.FullName == typeof(Debug).FullName)
+                {
+                    debugTypeDef = unityTypeDef;
+                    continue;
+                }
+            }
+
+            TypeDefinition networkManagerTypeDef = null;
+            TypeDefinition networkBehaviourTypeDef = null;
+            TypeDefinition networkHandlerDelegateTypeDef = null;
+            TypeDefinition rpcParamsTypeDef = null;
+            TypeDefinition serverRpcParamsTypeDef = null;
+            TypeDefinition clientRpcParamsTypeDef = null;
+            TypeDefinition fastBufferWriterTypeDef = null;
+            TypeDefinition fastBufferReaderTypeDef = null;
+            TypeDefinition networkVariableSerializationTypesTypeDef = null;
+            TypeDefinition bytePackerTypeDef = null;
+            TypeDefinition byteUnpackerTypeDef = null;
+            foreach (var netcodeTypeDef in m_NetcodeModule.GetAllTypes())
+            {
+                if (networkManagerTypeDef == null && netcodeTypeDef.Name == nameof(NetworkManager))
+                {
+                    networkManagerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkBehaviourTypeDef == null && netcodeTypeDef.Name == nameof(NetworkBehaviour))
+                {
+                    networkBehaviourTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkHandlerDelegateTypeDef == null && netcodeTypeDef.Name == nameof(NetworkManager.RpcReceiveHandler))
+                {
+                    networkHandlerDelegateTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (rpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(__RpcParams))
+                {
+                    rpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (serverRpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(ServerRpcParams))
+                {
+                    serverRpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (clientRpcParamsTypeDef == null && netcodeTypeDef.Name == nameof(ClientRpcParams))
+                {
+                    clientRpcParamsTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (fastBufferWriterTypeDef == null && netcodeTypeDef.Name == nameof(FastBufferWriter))
+                {
+                    fastBufferWriterTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (fastBufferReaderTypeDef == null && netcodeTypeDef.Name == nameof(FastBufferReader))
+                {
+                    fastBufferReaderTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (networkVariableSerializationTypesTypeDef == null && netcodeTypeDef.Name == nameof(NetworkVariableSerializationTypes))
+                {
+                    networkVariableSerializationTypesTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (bytePackerTypeDef == null && netcodeTypeDef.Name == nameof(BytePacker))
+                {
+                    bytePackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+
+                if (byteUnpackerTypeDef == null && netcodeTypeDef.Name == nameof(ByteUnpacker))
+                {
+                    byteUnpackerTypeDef = netcodeTypeDef;
+                    continue;
+                }
+            }
+
+            foreach (var methodDef in debugTypeDef.Methods)
+            {
+                switch (methodDef.Name)
                 {
                     case k_Debug_LogError:
-                        if (methodInfo.GetParameters().Length == 1)
+                        if (methodDef.Parameters.Count == 1)
                         {
-                            m_Debug_LogError_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                            m_Debug_LogError_MethodRef = moduleDefinition.ImportReference(methodDef);
                         }
 
                         break;
                 }
             }
 
-            var networkManagerType = typeof(NetworkManager);
+            m_NetworkManager_TypeRef = moduleDefinition.ImportReference(networkManagerTypeDef);
-            m_NetworkManager_TypeRef = moduleDefinition.ImportReference(networkManagerType);
+            foreach (var propertyDef in networkManagerTypeDef.Properties)
-            foreach (var propertyInfo in networkManagerType.GetProperties())
             {
-                switch (propertyInfo.Name)
+                switch (propertyDef.Name)
                 {
                     case k_NetworkManager_LocalClientId:
-                        m_NetworkManager_getLocalClientId_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getLocalClientId_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsListening:
-                        m_NetworkManager_getIsListening_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsListening_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsHost:
-                        m_NetworkManager_getIsHost_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsHost_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsServer:
-                        m_NetworkManager_getIsServer_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsServer_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkManager_IsClient:
-                        m_NetworkManager_getIsClient_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkManager_getIsClient_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                 }
             }
 
-            foreach (var fieldInfo in networkManagerType.GetFields(BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var fieldDef in networkManagerTypeDef.Fields)
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_NetworkManager_LogLevel:
-                        m_NetworkManager_LogLevel_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_LogLevel_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case k_NetworkManager_rpc_func_table:
-                        m_NetworkManager_rpc_func_table_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_rpc_func_table_FieldRef = moduleDefinition.ImportReference(fieldDef);
-                        m_NetworkManager_rpc_func_table_Add_MethodRef = moduleDefinition.ImportReference(fieldInfo.FieldType.GetMethod("Add"));
+
+                        m_NetworkManager_rpc_func_table_Add_MethodRef = fieldDef.FieldType.Resolve().Methods.First(m => m.Name == "Add");
+                        m_NetworkManager_rpc_func_table_Add_MethodRef.DeclaringType = fieldDef.FieldType;
+                        m_NetworkManager_rpc_func_table_Add_MethodRef = moduleDefinition.ImportReference(m_NetworkManager_rpc_func_table_Add_MethodRef);
                         break;
                     case k_NetworkManager_rpc_name_table:
-                        m_NetworkManager_rpc_name_table_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkManager_rpc_name_table_FieldRef = moduleDefinition.ImportReference(fieldDef);
-                        m_NetworkManager_rpc_name_table_Add_MethodRef = moduleDefinition.ImportReference(fieldInfo.FieldType.GetMethod("Add"));
+
+                        m_NetworkManager_rpc_name_table_Add_MethodRef = fieldDef.FieldType.Resolve().Methods.First(m => m.Name == "Add");
+                        m_NetworkManager_rpc_name_table_Add_MethodRef.DeclaringType = fieldDef.FieldType;
+                        m_NetworkManager_rpc_name_table_Add_MethodRef = moduleDefinition.ImportReference(m_NetworkManager_rpc_name_table_Add_MethodRef);
                         break;
                 }
             }
 
-            var networkBehaviourType = typeof(NetworkBehaviour);
+            m_NetworkBehaviour_TypeRef = moduleDefinition.ImportReference(networkBehaviourTypeDef);
-            m_NetworkBehaviour_TypeRef = moduleDefinition.ImportReference(networkBehaviourType);
+            foreach (var propertyDef in networkBehaviourTypeDef.Properties)
-            foreach (var propertyInfo in networkBehaviourType.GetProperties())
             {
-                switch (propertyInfo.Name)
+                switch (propertyDef.Name)
                 {
                     case k_NetworkBehaviour_NetworkManager:
-                        m_NetworkBehaviour_getNetworkManager_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkBehaviour_getNetworkManager_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                     case k_NetworkBehaviour_OwnerClientId:
-                        m_NetworkBehaviour_getOwnerClientId_MethodRef = moduleDefinition.ImportReference(propertyInfo.GetMethod);
+                        m_NetworkBehaviour_getOwnerClientId_MethodRef = moduleDefinition.ImportReference(propertyDef.GetMethod);
                         break;
                 }
             }
 
-            foreach (var methodInfo in networkBehaviourType.GetMethods(BindingFlags.Static | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var methodDef in networkBehaviourTypeDef.Methods)
             {
-                switch (methodInfo.Name)
+                switch (methodDef.Name)
                 {
                     case k_NetworkBehaviour_beginSendServerRpc:
-                        m_NetworkBehaviour_beginSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_beginSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_endSendServerRpc:
-                        m_NetworkBehaviour_endSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_endSendServerRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_beginSendClientRpc:
-                        m_NetworkBehaviour_beginSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_beginSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                     case k_NetworkBehaviour_endSendClientRpc:
-                        m_NetworkBehaviour_endSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodInfo);
+                        m_NetworkBehaviour_endSendClientRpc_MethodRef = moduleDefinition.ImportReference(methodDef);
                         break;
                 }
             }
 
-            foreach (var fieldInfo in networkBehaviourType.GetFields(BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public))
+            foreach (var fieldDef in networkBehaviourTypeDef.Fields)
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_NetworkBehaviour_rpc_exec_stage:
-                        m_NetworkBehaviour_rpc_exec_stage_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_NetworkBehaviour_rpc_exec_stage_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var networkHandlerDelegateType = typeof(NetworkManager.RpcReceiveHandler);
+            foreach (var ctor in networkHandlerDelegateTypeDef.Resolve().GetConstructors())
-            m_NetworkHandlerDelegateCtor_MethodRef = moduleDefinition.ImportReference(networkHandlerDelegateType.GetConstructor(new[] { typeof(object), typeof(IntPtr) }));
-
-            var rpcParamsType = typeof(__RpcParams);
-            m_RpcParams_TypeRef = moduleDefinition.ImportReference(rpcParamsType);
-            foreach (var fieldInfo in rpcParamsType.GetFields())
             {
-                switch (fieldInfo.Name)
+                if (ctor.HasParameters &&
+                    ctor.Parameters.Count == 2 &&
+                    ctor.Parameters[0].ParameterType.Name == nameof(System.Object) &&
+                    ctor.Parameters[1].ParameterType.Name == nameof(IntPtr))
+                {
+                    m_NetworkHandlerDelegateCtor_MethodRef = moduleDefinition.ImportReference(ctor);
+                    break;
+                }
+            }
+
+            m_RpcParams_TypeRef = moduleDefinition.ImportReference(rpcParamsTypeDef);
+            foreach (var fieldDef in rpcParamsTypeDef.Fields)
+            {
+                switch (fieldDef.Name)
                 {
                     case k_RpcParams_Server:
-                        m_RpcParams_Server_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_RpcParams_Server_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                     case k_RpcParams_Client:
-                        m_RpcParams_Client_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_RpcParams_Client_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var serverRpcParamsType = typeof(ServerRpcParams);
+            m_ServerRpcParams_TypeRef = moduleDefinition.ImportReference(serverRpcParamsTypeDef);
-            m_ServerRpcParams_TypeRef = moduleDefinition.ImportReference(serverRpcParamsType);
+            foreach (var fieldDef in serverRpcParamsTypeDef.Fields)
-            foreach (var fieldInfo in serverRpcParamsType.GetFields())
             {
-                switch (fieldInfo.Name)
+                switch (fieldDef.Name)
                 {
                     case k_ServerRpcParams_Receive:
-                        foreach (var recvFieldInfo in fieldInfo.FieldType.GetFields())
+                        foreach (var recvFieldDef in fieldDef.FieldType.Resolve().Fields)
                         {
-                            switch (recvFieldInfo.Name)
+                            switch (recvFieldDef.Name)
                             {
                                 case k_ServerRpcReceiveParams_SenderClientId:
-                                    m_ServerRpcParams_Receive_SenderClientId_FieldRef = moduleDefinition.ImportReference(recvFieldInfo);
+                                    m_ServerRpcParams_Receive_SenderClientId_FieldRef = moduleDefinition.ImportReference(recvFieldDef);
                                     break;
                             }
                         }
 
-                        m_ServerRpcParams_Receive_FieldRef = moduleDefinition.ImportReference(fieldInfo);
+                        m_ServerRpcParams_Receive_FieldRef = moduleDefinition.ImportReference(fieldDef);
                         break;
                 }
             }
 
-            var clientRpcParamsType = typeof(ClientRpcParams);
+            m_ClientRpcParams_TypeRef = moduleDefinition.ImportReference(clientRpcParamsTypeDef);
-            m_ClientRpcParams_TypeRef = moduleDefinition.ImportReference(clientRpcParamsType);
+            m_FastBufferWriter_TypeRef = moduleDefinition.ImportReference(fastBufferWriterTypeDef);
+            m_FastBufferReader_TypeRef = moduleDefinition.ImportReference(fastBufferReaderTypeDef);
 
-            var fastBufferWriterType = typeof(FastBufferWriter);
+            // Find all extension methods for FastBufferReader and FastBufferWriter to enable user-implemented methods to be called
-            m_FastBufferWriter_TypeRef = moduleDefinition.ImportReference(fastBufferWriterType);
-
-            var fastBufferReaderType = typeof(FastBufferReader);
-            m_FastBufferReader_TypeRef = moduleDefinition.ImportReference(fastBufferReaderType);
-
-            // Find all extension methods for FastBufferReader and FastBufferWriter to enable user-implemented
-            // methods to be called.
             var assemblies = new List<AssemblyDefinition> { m_MainModule.Assembly };
             foreach (var reference in m_MainModule.AssemblyReferences)
             {
@@ -371,9 +673,222 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
+            foreach (var method in networkVariableSerializationTypesTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_UnmanagedByMemcpy):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedByMemcpy_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_UnmanagedINetworkSerializable):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_UnmanagedINetworkSerializable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_ManagedINetworkSerializable):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_ManagedINetworkSerializable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeSerializer_FixedString):
+                        m_NetworkVariableSerializationTypes_InitializeSerializer_FixedString_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_ManagedIEquatable):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedIEquatable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_UnmanagedIEquatable):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedIEquatable_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_UnmanagedValueEquals):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_UnmanagedValueEquals_MethodRef = method;
+                        break;
+                    case nameof(NetworkVariableSerializationTypes.InitializeEqualityChecker_ManagedClassEquals):
+                        m_NetworkVariableSerializationTypes_InitializeEqualityChecker_ManagedClassEquals_MethodRef = method;
+                        break;
+                }
+            }
+
+            foreach (var method in bytePackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(BytePacker.WriteValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).FullName)
+                        {
+                            m_BytePacker_WriteValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
+            foreach (var method in byteUnpackerTypeDef.Methods)
+            {
+                if (!method.IsStatic)
+                {
+                    continue;
+                }
+
+                switch (method.Name)
+                {
+                    case nameof(ByteUnpacker.ReadValueBitPacked):
+                        if (method.Parameters[1].ParameterType.FullName == typeof(short).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ushort).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(int).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(uint).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(long).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        else if (method.Parameters[1].ParameterType.FullName == typeof(ulong).MakeByRefType().FullName)
+                        {
+                            m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef = m_MainModule.ImportReference(method);
+                        }
+                        break;
+                }
+            }
+
             return true;
         }
 
+        // This gets all fields from this type as well as any parent types, up to (but not including) the base NetworkBehaviour class
+        // Importantly... this also resolves any generics, so if the base class is Foo<T> and contains a field of NetworkVariable<T>,
+        // and this class is Bar : Foo<int>, it will properly resolve NetworkVariable<T> to NetworkVariable<int>.
+        private void GetAllFieldsAndResolveGenerics(TypeDefinition type, ref List<TypeReference> fieldTypes, Dictionary<string, TypeReference> genericParameters = null)
+        {
+            foreach (var field in type.Fields)
+            {
+                if (field.FieldType.IsGenericInstance)
+                {
+                    var genericType = (GenericInstanceType)field.FieldType;
+                    var newGenericType = new GenericInstanceType(field.FieldType.Resolve());
+                    for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                    {
+                        var argument = genericType.GenericArguments[i];
+
+                        if (genericParameters != null && genericParameters.ContainsKey(argument.Name))
+                        {
+                            newGenericType.GenericArguments.Add(genericParameters[argument.Name]);
+                        }
+                        else
+                        {
+                            newGenericType.GenericArguments.Add(argument);
+                        }
+                    }
+                    fieldTypes.Add(newGenericType);
+                }
+                else
+                {
+                    fieldTypes.Add(field.FieldType);
+                }
+            }
+
+            if (type.BaseType == null || type.BaseType.Name == nameof(NetworkBehaviour))
+            {
+                return;
+            }
+            var genericParams = new Dictionary<string, TypeReference>();
+            var resolved = type.BaseType.Resolve();
+            if (type.BaseType.IsGenericInstance)
+            {
+                var genericType = (GenericInstanceType)type.BaseType;
+                for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                {
+                    genericParams[resolved.GenericParameters[i].Name] = genericType.GenericArguments[i];
+                }
+            }
+            GetAllFieldsAndResolveGenerics(resolved, ref fieldTypes, genericParams);
+        }
+
+        private void GetAllBaseTypesAndResolveGenerics(TypeDefinition type, ref List<TypeReference> baseTypes, Dictionary<string, TypeReference> genericParameters)
+        {
+
+            if (type == null || type.BaseType == null || type.BaseType.Name == "Object")
+            {
+                return;
+            }
+
+            var baseType = type.BaseType;
+
+            var genericParams = new Dictionary<string, TypeReference>();
+
+            if (baseType.IsGenericInstance)
+            {
+                var genericType = (GenericInstanceType)baseType;
+                var newGenericType = new GenericInstanceType(baseType.Resolve());
+                for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                {
+                    var argument = genericType.GenericArguments[i];
+
+                    if (genericParameters != null && genericParameters.ContainsKey(argument.Name))
+                    {
+                        newGenericType.GenericArguments.Add(genericParameters[argument.Name]);
+                        genericParams[baseType.Resolve().GenericParameters[newGenericType.GenericArguments.Count - 1].Name] = genericParameters[argument.Name];
+                    }
+                    else
+                    {
+                        newGenericType.GenericArguments.Add(argument);
+                    }
+                }
+                baseTypes.Add(newGenericType);
+            }
+            else
+            {
+                baseTypes.Add(baseType);
+            }
+
+            var resolved = type.BaseType.Resolve();
+            if (type.BaseType.IsGenericInstance)
+            {
+                var genericType = (GenericInstanceType)type.BaseType;
+                for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                {
+                    if (!genericParams.ContainsKey(resolved.GenericParameters[i].Name))
+                    {
+                        genericParams[resolved.GenericParameters[i].Name] = genericType.GenericArguments[i];
+                    }
+                }
+            }
+            GetAllBaseTypesAndResolveGenerics(resolved, ref baseTypes, genericParams);
+        }
+
         private void ProcessNetworkBehaviour(TypeDefinition typeDefinition, string[] assemblyDefines)
         {
             var rpcHandlers = new List<(uint RpcMethodId, MethodDefinition RpcHandler)>();
@@ -416,6 +931,56 @@ namespace Unity.Netcode.Editor.CodeGen
                 }
             }
 
+            if (!typeDefinition.HasGenericParameters && !typeDefinition.IsGenericInstance)
+            {
+                var fieldTypes = new List<TypeReference>();
+                GetAllFieldsAndResolveGenerics(typeDefinition, ref fieldTypes);
+                foreach (var type in fieldTypes)
+                {
+                    //var type = field.FieldType;
+                    if (type.IsGenericInstance)
+                    {
+                        if (type.Resolve().Name == typeof(NetworkVariable<>).Name || type.Resolve().Name == typeof(NetworkList<>).Name)
+                        {
+                            var genericInstanceType = (GenericInstanceType)type;
+                            var wrappedType = genericInstanceType.GenericArguments[0];
+                            if (!m_WrappedNetworkVariableTypes.Contains(wrappedType))
+                            {
+                                m_WrappedNetworkVariableTypes.Add(wrappedType);
+                            }
+                        }
+                    }
+                    {
+                        var baseTypes = new List<TypeReference>();
+
+                        var genericParams = new Dictionary<string, TypeReference>();
+                        var resolved = type.Resolve();
+                        if (type.IsGenericInstance)
+                        {
+                            var genericType = (GenericInstanceType)type;
+                            for (var i = 0; i < genericType.GenericArguments.Count; ++i)
+                            {
+                                genericParams[resolved.GenericParameters[i].Name] = genericType.GenericArguments[i];
+                            }
+                        }
+
+                        GetAllBaseTypesAndResolveGenerics(type.Resolve(), ref baseTypes, genericParams);
+                        foreach (var baseType in baseTypes)
+                        {
+                            if (baseType.Resolve().Name == typeof(NetworkVariable<>).Name || baseType.Resolve().Name == typeof(NetworkList<>).Name)
+                            {
+                                var genericInstanceType = (GenericInstanceType)baseType;
+                                var wrappedType = genericInstanceType.GenericArguments[0];
+                                if (!m_WrappedNetworkVariableTypes.Contains(wrappedType))
+                                {
+                                    m_WrappedNetworkVariableTypes.Add(wrappedType);
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
             if (rpcHandlers.Count > 0 || rpcNames.Count > 0)
             {
                 var staticCtorMethodDef = typeDefinition.GetStaticConstructor();
@@ -656,6 +1221,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetWriteMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_BytePacker_WriteValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
             var foundMethodRef = m_FastBufferWriter_WriteValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);
 
@@ -669,7 +1264,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     {
                         if (parameters[1].IsIn)
                         {
-                            if (parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve() &&
+                            if (((ByReferenceType)parameters[1].ParameterType).ElementType.FullName == paramType.FullName &&
                                 ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
@@ -679,8 +1274,7 @@ namespace Unity.Netcode.Editor.CodeGen
                         }
                         else
                         {
-
+                            if (parameters[1].ParameterType.FullName == paramType.FullName &&
-                            if (parameters[1].ParameterType.Resolve() == paramType.Resolve() &&
                                 parameters[1].ParameterType.IsArray == paramType.IsArray)
                             {
                                 methodRef = method;
@@ -803,6 +1397,36 @@ namespace Unity.Netcode.Editor.CodeGen
 
         private bool GetReadMethodForParameter(TypeReference paramType, out MethodReference methodRef)
         {
+            if (paramType.FullName == typeof(short).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Short_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ushort).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UShort_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(int).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Int_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(uint).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_UInt_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(long).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_Long_MethodRef;
+                return true;
+            }
+            if (paramType.FullName == typeof(ulong).FullName)
+            {
+                methodRef = m_ByteUnpacker_ReadValueBitPacked_ULong_MethodRef;
+                return true;
+            }
             var assemblyQualifiedName = paramType.FullName + ", " + paramType.Resolve().Module.Assembly.FullName;
 
             var foundMethodRef = m_FastBufferReader_ReadValue_MethodRefs.TryGetValue(assemblyQualifiedName, out methodRef);
@@ -813,7 +1437,7 @@ namespace Unity.Netcode.Editor.CodeGen
                     var parameters = method.Resolve().Parameters;
                     if (method.Name == k_ReadValueMethodName &&
                         parameters[1].IsOut &&
-                        parameters[1].ParameterType.Resolve() == paramType.MakeByReferenceType().Resolve() &&
+                        ((ByReferenceType)parameters[1].ParameterType).ElementType.FullName == paramType.FullName &&
                         ((ByReferenceType)parameters[1].ParameterType).ElementType.IsArray == paramType.IsArray)
                     {
                         methodRef = method;

Editor/Configuration.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: b2f70916f7024c66aa5dfe1e43c151a2
+timeCreated: 1654274400

Editor/Configuration/NetcodeForGameObjectsSettings.cs

@@ -0,0 +1,53 @@
+using UnityEditor;
+using UnityEngine;
+
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal class NetcodeForGameObjectsEditorSettings
+    {
+        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
+        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
+
+        internal static int GetNetcodeInstallMultiplayerToolTips()
+        {
+            if (EditorPrefs.HasKey(InstallMultiplayerToolsTipDismissedPlayerPrefKey))
+            {
+                return EditorPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey);
+            }
+
+            return 0;
+        }
+
+        internal static void SetNetcodeInstallMultiplayerToolTips(int toolTipPrefSetting)
+        {
+            EditorPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, toolTipPrefSetting);
+        }
+
+        internal static bool GetAutoAddNetworkObjectSetting()
+        {
+            if (EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists))
+            {
+                return EditorPrefs.GetBool(AutoAddNetworkObjectIfNoneExists);
+            }
+
+            return false;
+        }
+
+        internal static void SetAutoAddNetworkObjectSetting(bool autoAddSetting)
+        {
+            EditorPrefs.SetBool(AutoAddNetworkObjectIfNoneExists, autoAddSetting);
+        }
+    }
+
+    [FilePath("ProjectSettings/NetcodeForGameObjects.settings", FilePathAttribute.Location.ProjectFolder)]
+    internal class NetcodeForGameObjectsProjectSettings : ScriptableSingleton<NetcodeForGameObjectsProjectSettings>
+    {
+        [SerializeField] public bool GenerateDefaultNetworkPrefabs = true;
+
+        internal void SaveSettings()
+        {
+            Save(true);
+        }
+    }
+}

Editor/Configuration/NetcodeForGameObjectsSettings.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 2f9c9b10bc41a0e46ab71324dd0ac6e1
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/Configuration/NetcodeSettingsProvider.cs

@@ -0,0 +1,179 @@
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    internal static class NetcodeSettingsProvider
+    {
+        private const float k_MaxLabelWidth = 450f;
+        private static float s_MaxLabelWidth;
+        private static bool s_ShowEditorSettingFields = true;
+        private static bool s_ShowProjectSettingFields = true;
+
+        [SettingsProvider]
+        public static SettingsProvider CreateNetcodeSettingsProvider()
+        {
+            // First parameter is the path in the Settings window.
+            // Second parameter is the scope of this setting: it only appears in the Settings window for the Project scope.
+            var provider = new SettingsProvider("Project/NetcodeForGameObjects", SettingsScope.Project)
+            {
+                label = "Netcode for GameObjects",
+                keywords = new[] { "netcode", "editor" },
+                guiHandler = OnGuiHandler,
+            };
+
+            return provider;
+        }
+
+
+        internal static NetcodeSettingsLabel NetworkObjectsSectionLabel;
+        internal static NetcodeSettingsToggle AutoAddNetworkObjectToggle;
+        internal static NetcodeSettingsLabel MultiplayerToolsLabel;
+        internal static NetcodeSettingsToggle MultiplayerToolTipStatusToggle;
+
+        /// <summary>
+        /// Creates an instance of the settings UI Elements if they don't already exist.
+        /// </summary>
+        /// <remarks>
+        /// We have to construct any NetcodeGUISettings derived classes here because in
+        /// version 2020.x.x EditorStyles.label does not exist yet (higher versions it does)
+        /// </remarks>
+        private static void CheckForInitialize()
+        {
+            if (NetworkObjectsSectionLabel == null)
+            {
+                NetworkObjectsSectionLabel = new NetcodeSettingsLabel("NetworkObject Helper Settings", 20);
+            }
+
+            if (AutoAddNetworkObjectToggle == null)
+            {
+                AutoAddNetworkObjectToggle = new NetcodeSettingsToggle("Auto-Add NetworkObject Component", "When enabled, NetworkObject components are automatically added to GameObjects when NetworkBehaviour components are added first.", 20);
+            }
+
+            if (MultiplayerToolsLabel == null)
+            {
+                MultiplayerToolsLabel = new NetcodeSettingsLabel("Multiplayer Tools", 20);
+            }
+
+            if (MultiplayerToolTipStatusToggle == null)
+            {
+                MultiplayerToolTipStatusToggle = new NetcodeSettingsToggle("Multiplayer Tools Install Reminder", "When enabled, the NetworkManager will display the notification to install the multiplayer tools package.", 20);
+            }
+        }
+
+        private static void OnGuiHandler(string obj)
+        {
+            // Make sure all NetcodeGUISettings derived classes are instantiated first
+            CheckForInitialize();
+
+            var autoAddNetworkObjectSetting = NetcodeForGameObjectsEditorSettings.GetAutoAddNetworkObjectSetting();
+            var multiplayerToolsTipStatus = NetcodeForGameObjectsEditorSettings.GetNetcodeInstallMultiplayerToolTips() == 0;
+            var settings = NetcodeForGameObjectsProjectSettings.instance;
+            var generateDefaultPrefabs = settings.GenerateDefaultNetworkPrefabs;
+
+            EditorGUI.BeginChangeCheck();
+
+            GUILayout.BeginVertical("Box");
+            s_ShowEditorSettingFields = EditorGUILayout.BeginFoldoutHeaderGroup(s_ShowEditorSettingFields, "Editor Settings");
+
+            if (s_ShowEditorSettingFields)
+            {
+                GUILayout.BeginVertical("Box");
+                NetworkObjectsSectionLabel.DrawLabel();
+                autoAddNetworkObjectSetting = AutoAddNetworkObjectToggle.DrawToggle(autoAddNetworkObjectSetting);
+                GUILayout.EndVertical();
+
+                GUILayout.BeginVertical("Box");
+                MultiplayerToolsLabel.DrawLabel();
+                multiplayerToolsTipStatus = MultiplayerToolTipStatusToggle.DrawToggle(multiplayerToolsTipStatus);
+                GUILayout.EndVertical();
+            }
+            EditorGUILayout.EndFoldoutHeaderGroup();
+            GUILayout.EndVertical();
+
+            GUILayout.BeginVertical("Box");
+            s_ShowProjectSettingFields = EditorGUILayout.BeginFoldoutHeaderGroup(s_ShowProjectSettingFields, "Project Settings");
+            if (s_ShowProjectSettingFields)
+            {
+                GUILayout.BeginVertical("Box");
+                const string generateNetworkPrefabsString = "Generate Default Network Prefabs List";
+
+                if (s_MaxLabelWidth == 0)
+                {
+                    s_MaxLabelWidth = EditorStyles.label.CalcSize(new GUIContent(generateNetworkPrefabsString)).x;
+                    s_MaxLabelWidth = Mathf.Min(k_MaxLabelWidth, s_MaxLabelWidth);
+                }
+
+                EditorGUIUtility.labelWidth = s_MaxLabelWidth;
+
+                GUILayout.Label("Network Prefabs", EditorStyles.boldLabel);
+                generateDefaultPrefabs = EditorGUILayout.Toggle(
+                    new GUIContent(
+                        generateNetworkPrefabsString,
+                        "When enabled, a default NetworkPrefabsList object will be added to your project and kept up " +
+                        "to date with all NetworkObject prefabs."),
+                    generateDefaultPrefabs,
+                    GUILayout.Width(s_MaxLabelWidth + 20));
+                GUILayout.EndVertical();
+            }
+            EditorGUILayout.EndFoldoutHeaderGroup();
+            GUILayout.EndVertical();
+            if (EditorGUI.EndChangeCheck())
+            {
+                NetcodeForGameObjectsEditorSettings.SetAutoAddNetworkObjectSetting(autoAddNetworkObjectSetting);
+                NetcodeForGameObjectsEditorSettings.SetNetcodeInstallMultiplayerToolTips(multiplayerToolsTipStatus ? 0 : 1);
+                settings.GenerateDefaultNetworkPrefabs = generateDefaultPrefabs;
+                settings.SaveSettings();
+            }
+        }
+    }
+
+    internal class NetcodeSettingsLabel : NetcodeGUISettings
+    {
+        private string m_LabelContent;
+
+        public void DrawLabel()
+        {
+            EditorGUIUtility.labelWidth = m_LabelSize;
+            GUILayout.Label(m_LabelContent, EditorStyles.boldLabel, m_LayoutWidth);
+        }
+
+        public NetcodeSettingsLabel(string labelText, float layoutOffset = 0.0f)
+        {
+            m_LabelContent = labelText;
+            AdjustLabelSize(labelText, layoutOffset);
+        }
+    }
+
+    internal class NetcodeSettingsToggle : NetcodeGUISettings
+    {
+        private GUIContent m_ToggleContent;
+
+        public bool DrawToggle(bool currentSetting)
+        {
+            EditorGUIUtility.labelWidth = m_LabelSize;
+            return EditorGUILayout.Toggle(m_ToggleContent, currentSetting, m_LayoutWidth);
+        }
+
+        public NetcodeSettingsToggle(string labelText, string toolTip, float layoutOffset)
+        {
+            AdjustLabelSize(labelText, layoutOffset);
+            m_ToggleContent = new GUIContent(labelText, toolTip);
+        }
+    }
+
+    internal class NetcodeGUISettings
+    {
+        private const float k_MaxLabelWidth = 450f;
+        protected float m_LabelSize { get; private set; }
+
+        protected GUILayoutOption m_LayoutWidth { get; private set; }
+
+        protected void AdjustLabelSize(string labelText, float offset = 0.0f)
+        {
+            m_LabelSize = Mathf.Min(k_MaxLabelWidth, EditorStyles.label.CalcSize(new GUIContent(labelText)).x);
+            m_LayoutWidth = GUILayout.Width(m_LabelSize + offset);
+        }
+    }
+
+}

Editor/Configuration/NetcodeSettingsProvider.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 6b373a89fcbd41444a97ebd1798b326f
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/Configuration/NetworkPrefabProcessor.cs

@@ -0,0 +1,187 @@
+using System.Collections.Generic;
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor.Configuration
+{
+    /// <summary>
+    /// Updates the default <see cref="NetworkPrefabsList"/> instance when prefabs are updated (created, moved, deleted) in the project.
+    /// </summary>
+    public class NetworkPrefabProcessor : AssetPostprocessor
+    {
+        private static string s_DefaultNetworkPrefabsPath = "Assets/DefaultNetworkPrefabs.asset";
+        public static string DefaultNetworkPrefabsPath
+        {
+            get
+            {
+                return s_DefaultNetworkPrefabsPath;
+            }
+            internal set
+            {
+                s_DefaultNetworkPrefabsPath = value;
+                // Force a recache of the prefab list
+                s_PrefabsList = null;
+            }
+        }
+        private static NetworkPrefabsList s_PrefabsList;
+        private static Dictionary<string, NetworkPrefab> s_PrefabsListPath = new Dictionary<string, NetworkPrefab>();
+
+        private static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths)
+        {
+            var settings = NetcodeForGameObjectsProjectSettings.instance;
+            if (!settings.GenerateDefaultNetworkPrefabs)
+            {
+                return;
+            }
+
+            bool ProcessImportedAssets(string[] importedAssets1)
+            {
+                var dirty = false;
+                foreach (var assetPath in importedAssets1)
+                {
+                    // We only care about GameObjects, skip everything else. Can't use the more targeted
+                    // OnPostProcessPrefabs since that's not called for moves or deletes
+                    if (AssetDatabase.GetMainAssetTypeAtPath(assetPath) != typeof(GameObject))
+                    {
+                        continue;
+                    }
+
+                    var go = AssetDatabase.LoadAssetAtPath<GameObject>(assetPath);
+                    if (go.TryGetComponent<NetworkObject>(out _))
+                    {
+                        // Make sure we are not duplicating an already existing entry
+                        if (s_PrefabsListPath.ContainsKey(assetPath))
+                        {
+                            // Is the imported asset different from the one we already have in the list?
+                            if (s_PrefabsListPath[assetPath].Prefab.GetHashCode() != go.GetHashCode())
+                            {
+                                // If so remove the one in the list and continue on to add the imported one
+                                s_PrefabsList.List.Remove(s_PrefabsListPath[assetPath]);
+                            }
+                            else // If they are identical, then just ignore the import
+                            {
+                                continue;
+                            }
+                        }
+
+                        s_PrefabsList.List.Add(new NetworkPrefab { Prefab = go });
+                        dirty = true;
+                    }
+                }
+
+                return dirty;
+            }
+
+            bool ProcessDeletedAssets(string[] strings)
+            {
+                var dirty = false;
+                var deleted = new List<string>(strings);
+                for (int i = s_PrefabsList.List.Count - 1; i >= 0 && deleted.Count > 0; --i)
+                {
+                    GameObject prefab;
+                    try
+                    {
+                        prefab = s_PrefabsList.List[i].Prefab;
+                    }
+                    catch (MissingReferenceException)
+                    {
+                        s_PrefabsList.List.RemoveAt(i);
+                        continue;
+                    }
+                    if (prefab == null)
+                    {
+                        s_PrefabsList.List.RemoveAt(i);
+                    }
+                    else
+                    {
+                        string noPath = AssetDatabase.GetAssetPath(prefab);
+                        for (int j = strings.Length - 1; j >= 0; --j)
+                        {
+                            if (noPath == strings[j])
+                            {
+                                s_PrefabsList.List.RemoveAt(i);
+                                deleted.RemoveAt(j);
+                                dirty = true;
+                            }
+                        }
+                    }
+                }
+
+                return dirty;
+            }
+
+            if (s_PrefabsList == null)
+            {
+                s_PrefabsList = GetOrCreateNetworkPrefabs(DefaultNetworkPrefabsPath, out var newList, true);
+                // A new list already processed all existing assets, no need to double-process imports & deletes
+                if (newList)
+                {
+                    return;
+                }
+            }
+            // Clear our asset path to prefab table each time
+            s_PrefabsListPath.Clear();
+
+            // Create our asst path to prefab table
+            foreach (var prefabEntry in s_PrefabsList.List)
+            {
+                if (!s_PrefabsListPath.ContainsKey(AssetDatabase.GetAssetPath(prefabEntry.Prefab)))
+                {
+                    s_PrefabsListPath.Add(AssetDatabase.GetAssetPath(prefabEntry.Prefab), prefabEntry);
+                }
+            }
+
+            // Process the imported and deleted assets
+            var markDirty = ProcessImportedAssets(importedAssets);
+            markDirty &= ProcessDeletedAssets(deletedAssets);
+
+            if (markDirty)
+            {
+                EditorUtility.SetDirty(s_PrefabsList);
+            }
+        }
+
+        internal static NetworkPrefabsList GetOrCreateNetworkPrefabs(string path, out bool isNew, bool addAll)
+        {
+            var defaultPrefabs = AssetDatabase.LoadAssetAtPath<NetworkPrefabsList>(path);
+            if (defaultPrefabs == null)
+            {
+                isNew = true;
+                defaultPrefabs = ScriptableObject.CreateInstance<NetworkPrefabsList>();
+                defaultPrefabs.IsDefault = true;
+                AssetDatabase.CreateAsset(defaultPrefabs, path);
+
+                if (addAll)
+                {
+                    // This could be very expensive in large projects... maybe make it manually triggered via a menu?
+                    defaultPrefabs.List = FindAll();
+                }
+                EditorUtility.SetDirty(defaultPrefabs);
+                AssetDatabase.SaveAssetIfDirty(defaultPrefabs);
+                return defaultPrefabs;
+            }
+
+            isNew = false;
+            return defaultPrefabs;
+        }
+
+        private static List<NetworkPrefab> FindAll()
+        {
+            var list = new List<NetworkPrefab>();
+
+            string[] guids = AssetDatabase.FindAssets("t:GameObject");
+            foreach (var guid in guids)
+            {
+                string assetPath = AssetDatabase.GUIDToAssetPath(guid);
+                var go = AssetDatabase.LoadAssetAtPath<GameObject>(assetPath);
+
+                if (go.TryGetComponent(out NetworkObject _))
+                {
+                    list.Add(new NetworkPrefab { Prefab = go });
+                }
+            }
+
+            return list;
+        }
+    }
+}

Editor/Configuration/NetworkPrefabProcessor.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d8b62a05d80cc444f9c74731c01b8e39
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/Configuration/NetworkPrefabsEditor.cs

@@ -0,0 +1,97 @@
+using UnityEditor;
+using UnityEditorInternal;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor
+{
+    [CustomEditor(typeof(NetworkPrefabsList), true)]
+    [CanEditMultipleObjects]
+    public class NetworkPrefabsEditor : UnityEditor.Editor
+    {
+        private ReorderableList m_NetworkPrefabsList;
+        private SerializedProperty m_IsDefaultBool;
+
+        private void OnEnable()
+        {
+            m_IsDefaultBool = serializedObject.FindProperty(nameof(NetworkPrefabsList.IsDefault));
+            m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty("List"), true, true, true, true);
+            m_NetworkPrefabsList.elementHeightCallback = index =>
+            {
+                var networkOverrideInt = 0;
+                if (m_NetworkPrefabsList.count > 0)
+                {
+                    var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
+                    var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
+                    networkOverrideInt = networkOverrideProp.enumValueIndex;
+                }
+
+                return 8 + (networkOverrideInt == 0 ? EditorGUIUtility.singleLineHeight : (EditorGUIUtility.singleLineHeight * 2) + 5);
+            };
+            m_NetworkPrefabsList.drawElementCallback = (rect, index, isActive, isFocused) =>
+            {
+                rect.y += 5;
+
+                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
+                var networkPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Prefab));
+                var networkSourceHashProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourceHashToOverride));
+                var networkSourcePrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourcePrefabToOverride));
+                var networkTargetPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.OverridingTargetPrefab));
+                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
+                var networkOverrideInt = networkOverrideProp.enumValueIndex;
+                var networkOverrideEnum = (NetworkPrefabOverride)networkOverrideInt;
+                EditorGUI.LabelField(new Rect(rect.x + rect.width - 70, rect.y, 60, EditorGUIUtility.singleLineHeight), "Override");
+                if (networkOverrideEnum == NetworkPrefabOverride.None)
+                {
+                    if (EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), false))
+                    {
+                        networkOverrideProp.enumValueIndex = (int)NetworkPrefabOverride.Prefab;
+                    }
+                }
+                else
+                {
+                    if (!EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), true))
+                    {
+                        networkOverrideProp.enumValueIndex = 0;
+                        networkOverrideEnum = NetworkPrefabOverride.None;
+                    }
+                }
+
+                if (networkOverrideEnum == NetworkPrefabOverride.None)
+                {
+                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width - 80, EditorGUIUtility.singleLineHeight), networkPrefabProp, GUIContent.none);
+                }
+                else
+                {
+                    networkOverrideProp.enumValueIndex = GUI.Toolbar(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), networkOverrideInt - 1, new[] { "Prefab", "Hash" }) + 1;
+
+                    if (networkOverrideEnum == NetworkPrefabOverride.Prefab)
+                    {
+                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourcePrefabProp, GUIContent.none);
+                    }
+                    else
+                    {
+                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourceHashProp, GUIContent.none);
+                    }
+
+                    rect.y += EditorGUIUtility.singleLineHeight + 5;
+
+                    EditorGUI.LabelField(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), "Overriding Prefab");
+                    EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 110, EditorGUIUtility.singleLineHeight), networkTargetPrefabProp, GUIContent.none);
+                }
+            };
+            m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
+        }
+
+        public override void OnInspectorGUI()
+        {
+            using (new EditorGUI.DisabledScope(true))
+            {
+                EditorGUILayout.PropertyField(m_IsDefaultBool);
+            }
+
+            m_NetworkPrefabsList.DoLayoutList();
+
+            serializedObject.ApplyModifiedProperties();
+        }
+    }
+}

Editor/Configuration/NetworkPrefabsEditor.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 8d6d0919fa8ff41c9b1d1241256f7364
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/HiddenScriptEditor.cs

@@ -0,0 +1,184 @@
+using Unity.Netcode.Components;
+#if UNITY_UNET_PRESENT
+using Unity.Netcode.Transports.UNET;
+#endif
+using Unity.Netcode.Transports.UTP;
+using UnityEditor;
+using UnityEngine;
+
+namespace Unity.Netcode.Editor
+{
+    /// <summary>
+    /// Internal use. Hides the script field for the given component.
+    /// </summary>
+    public class HiddenScriptEditor : UnityEditor.Editor
+    {
+        private static readonly string[] k_HiddenFields = { "m_Script" };
+
+        /// <summary>
+        /// Draws inspector properties without the script field.
+        /// </summary>
+        public override void OnInspectorGUI()
+        {
+            EditorGUI.BeginChangeCheck();
+            serializedObject.UpdateIfRequiredOrScript();
+            DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+            serializedObject.ApplyModifiedProperties();
+            EditorGUI.EndChangeCheck();
+        }
+    }
+#if UNITY_UNET_PRESENT
+    /// <summary>
+    /// Internal use. Hides the script field for UNetTransport.
+    /// </summary>
+    [CustomEditor(typeof(UNetTransport), true)]
+    public class UNetTransportEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+    /// <summary>
+    /// Internal use. Hides the script field for UnityTransport.
+    /// </summary>
+    [CustomEditor(typeof(UnityTransport), true)]
+    public class UnityTransportEditor : HiddenScriptEditor
+    {
+        private static readonly string[] k_HiddenFields = { "m_Script", "ConnectionData" };
+
+        private bool m_AllowIncomingConnections;
+        private bool m_Initialized;
+
+        private UnityTransport m_UnityTransport;
+
+        private SerializedProperty m_ServerAddressProperty;
+        private SerializedProperty m_ServerPortProperty;
+        private SerializedProperty m_OverrideBindIpProperty;
+
+        private const string k_LoopbackIpv4 = "127.0.0.1";
+        private const string k_LoopbackIpv6 = "::1";
+        private const string k_AnyIpv4 = "0.0.0.0";
+        private const string k_AnyIpv6 = "::";
+
+
+        private void Initialize()
+        {
+            if (m_Initialized)
+            {
+                return;
+            }
+            m_Initialized = true;
+            m_UnityTransport = (UnityTransport)target;
+
+            var connectionDataProperty = serializedObject.FindProperty(nameof(UnityTransport.ConnectionData));
+
+            m_ServerAddressProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Address));
+            m_ServerPortProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.Port));
+            m_OverrideBindIpProperty = connectionDataProperty.FindPropertyRelative(nameof(UnityTransport.ConnectionAddressData.ServerListenAddress));
+        }
+
+        /// <summary>
+        /// Draws inspector properties without the script field.
+        /// </summary>
+        public override void OnInspectorGUI()
+        {
+            Initialize();
+            EditorGUI.BeginChangeCheck();
+            serializedObject.UpdateIfRequiredOrScript();
+            DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+            serializedObject.ApplyModifiedProperties();
+            EditorGUI.EndChangeCheck();
+
+            EditorGUILayout.PropertyField(m_ServerAddressProperty);
+            EditorGUILayout.PropertyField(m_ServerPortProperty);
+
+            serializedObject.ApplyModifiedProperties();
+
+            EditorGUILayout.HelpBox("It's recommended to leave remote connections disabled for local testing to avoid exposing ports on your device.", MessageType.Info);
+            bool allowRemoteConnections = m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6 && !string.IsNullOrEmpty(m_UnityTransport.ConnectionData.ServerListenAddress);
+            allowRemoteConnections = EditorGUILayout.Toggle(new GUIContent("Allow Remote Connections?", $"Bind IP: {m_UnityTransport.ConnectionData.ServerListenAddress}"), allowRemoteConnections);
+
+            bool isIpV6 = m_UnityTransport.ConnectionData.IsIpv6;
+
+            if (!allowRemoteConnections)
+            {
+                if (m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv4 && m_UnityTransport.ConnectionData.ServerListenAddress != k_LoopbackIpv6)
+                {
+                    if (isIpV6)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv6;
+                    }
+                    else
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = k_LoopbackIpv4;
+                    }
+                    EditorUtility.SetDirty(m_UnityTransport);
+                }
+            }
+
+            using (new EditorGUI.DisabledScope(!allowRemoteConnections))
+            {
+                string overrideIp = m_UnityTransport.ConnectionData.ServerListenAddress;
+                if (overrideIp == k_AnyIpv4 || overrideIp == k_AnyIpv6 || overrideIp == k_LoopbackIpv4 || overrideIp == k_LoopbackIpv6)
+                {
+                    overrideIp = "";
+                }
+
+                overrideIp = EditorGUILayout.TextField("Override Bind IP (optional)", overrideIp);
+                if (allowRemoteConnections)
+                {
+                    if (overrideIp == "")
+                    {
+                        if (isIpV6)
+                        {
+                            overrideIp = k_AnyIpv6;
+                        }
+                        else
+                        {
+                            overrideIp = k_AnyIpv4;
+                        }
+                    }
+
+                    if (m_UnityTransport.ConnectionData.ServerListenAddress != overrideIp)
+                    {
+                        m_UnityTransport.ConnectionData.ServerListenAddress = overrideIp;
+                        EditorUtility.SetDirty(m_UnityTransport);
+                    }
+                }
+            }
+        }
+    }
+
+#if COM_UNITY_MODULES_ANIMATION
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkAnimator.
+    /// </summary>
+    [CustomEditor(typeof(NetworkAnimator), true)]
+    public class NetworkAnimatorEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+#if COM_UNITY_MODULES_PHYSICS
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkRigidbody.
+    /// </summary>
+    [CustomEditor(typeof(NetworkRigidbody), true)]
+    public class NetworkRigidbodyEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+
+#if COM_UNITY_MODULES_PHYSICS2D
+    /// <summary>
+    /// Internal use. Hides the script field for NetworkRigidbody2D.
+    /// </summary>
+    [CustomEditor(typeof(NetworkRigidbody2D), true)]
+    public class NetworkRigidbody2DEditor : HiddenScriptEditor
+    {
+
+    }
+#endif
+}

Editor/HiddenScriptEditor.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: ebf622cc80e94f488e59caf8b7419f50
+timeCreated: 1661959406

Editor/NetworkBehaviourEditor.cs

@@ -1,11 +1,15 @@
 using System;
 using System.Collections.Generic;
 using System.Reflection;
-using UnityEngine;
+using Unity.Netcode.Editor.Configuration;
 using UnityEditor;
+using UnityEngine;
 
 namespace Unity.Netcode.Editor
 {
+    /// <summary>
+    /// The <see cref="CustomEditor"/> for <see cref="NetworkBehaviour"/>
+    /// </summary>
     [CustomEditor(typeof(NetworkBehaviour), true)]
     [CanEditMultipleObjects]
     public class NetworkBehaviourEditor : UnityEditor.Editor
@@ -16,6 +20,7 @@ namespace Unity.Netcode.Editor
         private readonly Dictionary<string, object> m_NetworkVariableObjects = new Dictionary<string, object>();
 
         private GUIContent m_NetworkVariableLabelGuiContent;
+        private GUIContent m_NetworkListLabelGuiContent;
 
         private void Init(MonoScript script)
         {
@@ -26,6 +31,7 @@ namespace Unity.Netcode.Editor
             m_NetworkVariableObjects.Clear();
 
             m_NetworkVariableLabelGuiContent = new GUIContent("NetworkVariable", "This variable is a NetworkVariable. It can not be serialized and can only be changed during runtime.");
+            m_NetworkListLabelGuiContent = new GUIContent("NetworkList", "This variable is a NetworkList. It is rendered, but you can't serialize or change it.");
 
             var fields = script.GetClass().GetFields(BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy);
             for (int i = 0; i < fields.Length; i++)
@@ -33,8 +39,15 @@ namespace Unity.Netcode.Editor
                 var ft = fields[i].FieldType;
                 if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkVariable<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
                 {
-                    m_NetworkVariableNames.Add(fields[i].Name);
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
-                    m_NetworkVariableFields.Add(fields[i].Name, fields[i]);
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkVariable {fields[i].Name}");
+                }
+                if (ft.IsGenericType && ft.GetGenericTypeDefinition() == typeof(NetworkList<>) && !fields[i].IsDefined(typeof(HideInInspector), true))
+                {
+                    m_NetworkVariableNames.Add(ObjectNames.NicifyVariableName(fields[i].Name));
+                    m_NetworkVariableFields.Add(ObjectNames.NicifyVariableName(fields[i].Name), fields[i]);
+                    Debug.Log($"Adding NetworkList {fields[i].Name}");
                 }
             }
         }
@@ -68,25 +81,48 @@ namespace Unity.Netcode.Editor
             EditorGUILayout.BeginHorizontal();
             if (genericType.IsValueType)
             {
-                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkVariableValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
+                var method = typeof(NetworkBehaviourEditor).GetMethod("RenderNetworkContainerValueType", BindingFlags.Public | BindingFlags.Instance | BindingFlags.FlattenHierarchy | BindingFlags.NonPublic);
                 var genericMethod = method.MakeGenericMethod(genericType);
                 genericMethod.Invoke(this, new[] { (object)index });
             }
             else
             {
                 EditorGUILayout.LabelField("Type not renderable");
-            }
 
                 GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
                 EditorGUILayout.EndHorizontal();
             }
+        }
 
-        private void RenderNetworkVariableValueType<T>(int index) where T : unmanaged
+        private void RenderNetworkContainerValueType<T>(int index) where T : unmanaged, IEquatable<T>
+        {
+            try
             {
                 var networkVariable = (NetworkVariable<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                RenderNetworkVariableValueType(index, networkVariable);
+            }
+            catch (Exception)
+            {
+                try
+                {
+                    var networkList = (NetworkList<T>)m_NetworkVariableFields[m_NetworkVariableNames[index]].GetValue(target);
+                    RenderNetworkListValueType(index, networkList);
+                }
+                catch (Exception e)
+                {
+                    Debug.Log(e);
+                    throw;
+                }
+            }
+
+            EditorGUILayout.EndHorizontal();
+        }
+
+        private void RenderNetworkVariableValueType<T>(int index, NetworkVariable<T> networkVariable) where T : unmanaged
+        {
             var type = typeof(T);
             object val = networkVariable.Value;
-            string name = m_NetworkVariableNames[index];
+            string variableName = m_NetworkVariableNames[index];
 
             var behaviour = (NetworkBehaviour)target;
 
@@ -95,47 +131,51 @@ namespace Unity.Netcode.Editor
             {
                 if (type == typeof(int))
                 {
-                    val = EditorGUILayout.IntField(name, (int)val);
+                    val = EditorGUILayout.IntField(variableName, (int)val);
                 }
                 else if (type == typeof(uint))
                 {
-                    val = (uint)EditorGUILayout.LongField(name, (long)((uint)val));
+                    val = (uint)EditorGUILayout.LongField(variableName, (uint)val);
                 }
                 else if (type == typeof(short))
                 {
-                    val = (short)EditorGUILayout.IntField(name, (int)((short)val));
+                    val = (short)EditorGUILayout.IntField(variableName, (short)val);
                 }
                 else if (type == typeof(ushort))
                 {
-                    val = (ushort)EditorGUILayout.IntField(name, (int)((ushort)val));
+                    val = (ushort)EditorGUILayout.IntField(variableName, (ushort)val);
                 }
                 else if (type == typeof(sbyte))
                 {
-                    val = (sbyte)EditorGUILayout.IntField(name, (int)((sbyte)val));
+                    val = (sbyte)EditorGUILayout.IntField(variableName, (sbyte)val);
                 }
                 else if (type == typeof(byte))
                 {
-                    val = (byte)EditorGUILayout.IntField(name, (int)((byte)val));
+                    val = (byte)EditorGUILayout.IntField(variableName, (byte)val);
                 }
                 else if (type == typeof(long))
                 {
-                    val = EditorGUILayout.LongField(name, (long)val);
+                    val = EditorGUILayout.LongField(variableName, (long)val);
                 }
                 else if (type == typeof(ulong))
                 {
-                    val = (ulong)EditorGUILayout.LongField(name, (long)((ulong)val));
+                    val = (ulong)EditorGUILayout.LongField(variableName, (long)((ulong)val));
+                }
+                else if (type == typeof(float))
+                {
+                    val = EditorGUILayout.FloatField(variableName, (float)((float)val));
                 }
                 else if (type == typeof(bool))
                 {
-                    val = EditorGUILayout.Toggle(name, (bool)val);
+                    val = EditorGUILayout.Toggle(variableName, (bool)val);
                 }
                 else if (type == typeof(string))
                 {
-                    val = EditorGUILayout.TextField(name, (string)val);
+                    val = EditorGUILayout.TextField(variableName, (string)val);
                 }
                 else if (type.IsEnum)
                 {
-                    val = EditorGUILayout.EnumPopup(name, (Enum)val);
+                    val = EditorGUILayout.EnumPopup(variableName, (Enum)val);
                 }
                 else
                 {
@@ -146,11 +186,31 @@ namespace Unity.Netcode.Editor
             }
             else
             {
-                EditorGUILayout.LabelField(name, EditorStyles.wordWrappedLabel);
+                EditorGUILayout.LabelField(variableName, EditorStyles.wordWrappedLabel);
                 EditorGUILayout.SelectableLabel(val.ToString(), EditorStyles.wordWrappedLabel);
             }
+            GUILayout.Label(m_NetworkVariableLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkVariableLabelGuiContent).x));
         }
 
+        private void RenderNetworkListValueType<T>(int index, NetworkList<T> networkList)
+            where T : unmanaged, IEquatable<T>
+        {
+            string variableName = m_NetworkVariableNames[index];
+
+            string value = "";
+            bool addComma = false;
+            foreach (var v in networkList)
+            {
+                if (addComma)
+                {
+                    value += ", ";
+                }
+                value += v.ToString();
+                addComma = true;
+            }
+            EditorGUILayout.LabelField(variableName, value);
+            GUILayout.Label(m_NetworkListLabelGuiContent, EditorStyles.miniLabel, GUILayout.Width(EditorStyles.miniLabel.CalcSize(m_NetworkListLabelGuiContent).x));
+        }
 
         /// <inheritdoc/>
         public override void OnInspectorGUI()
@@ -230,8 +290,6 @@ namespace Unity.Netcode.Editor
             CheckForNetworkObject((target as NetworkBehaviour).gameObject);
         }
 
-        internal const string AutoAddNetworkObjectIfNoneExists = "AutoAdd-NetworkObject-When-None-Exist";
-
         /// <summary>
         /// Recursively finds the root parent of a <see cref="Transform"/>
         /// </summary>
@@ -263,8 +321,7 @@ namespace Unity.Netcode.Editor
 
             // Now get the root parent transform to the current GameObject (or itself)
             var rootTransform = GetRootParentTransform(gameObject.transform);
-            var networkManager = rootTransform.GetComponent<NetworkManager>();
+            if (!rootTransform.TryGetComponent<NetworkManager>(out var networkManager))
-            if (networkManager == null)
             {
                 networkManager = rootTransform.GetComponentInChildren<NetworkManager>();
             }
@@ -299,8 +356,7 @@ namespace Unity.Netcode.Editor
 
             // Otherwise, check to see if there is any NetworkObject from the root GameObject down to all children.
             // If not, notify the user that NetworkBehaviours require that the relative GameObject has a NetworkObject component.
-            var networkObject = rootTransform.GetComponent<NetworkObject>();
+            if (!rootTransform.TryGetComponent<NetworkObject>(out var networkObject))
-            if (networkObject == null)
             {
                 networkObject = rootTransform.GetComponentInChildren<NetworkObject>();
 
@@ -310,7 +366,7 @@ namespace Unity.Netcode.Editor
                     // and the user has already turned "Auto-Add NetworkObject" on when first notified about the requirement
                     // then just send a reminder to the user why the NetworkObject they just deleted seemingly "re-appeared"
                     // again.
-                    if (networkObjectRemoved && EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists) && EditorPrefs.GetBool(AutoAddNetworkObjectIfNoneExists))
+                    if (networkObjectRemoved && NetcodeForGameObjectsEditorSettings.GetAutoAddNetworkObjectSetting())
                     {
                         Debug.LogWarning($"{gameObject.name} still has {nameof(NetworkBehaviour)}s and Auto-Add NetworkObjects is enabled. A NetworkObject is being added back to {gameObject.name}.");
                         Debug.Log($"To reset Auto-Add NetworkObjects: Select the Netcode->General->Reset Auto-Add NetworkObject menu item.");
@@ -319,7 +375,7 @@ namespace Unity.Netcode.Editor
                     // Notify and provide the option to add it one time, always add a NetworkObject, or do nothing and let the user manually add it
                     if (EditorUtility.DisplayDialog($"{nameof(NetworkBehaviour)}s require a {nameof(NetworkObject)}",
                     $"{gameObject.name} does not have a {nameof(NetworkObject)} component.  Would you like to add one now?", "Yes", "No (manually add it)",
-                    DialogOptOutDecisionType.ForThisMachine, AutoAddNetworkObjectIfNoneExists))
+                    DialogOptOutDecisionType.ForThisMachine, NetcodeForGameObjectsEditorSettings.AutoAddNetworkObjectIfNoneExists))
                     {
                         gameObject.AddComponent<NetworkObject>();
                         var activeScene = UnityEngine.SceneManagement.SceneManager.GetActiveScene();
@@ -329,20 +385,5 @@ namespace Unity.Netcode.Editor
                 }
             }
         }
-
-        /// <summary>
-        /// This allows users to reset the Auto-Add NetworkObject preference
-        /// so the next time they add a NetworkBehaviour to a GameObject without
-        /// a NetworkObject it will display the dialog box again and not
-        /// automatically add a NetworkObject.
-        /// </summary>
-        [MenuItem("Netcode/General/Reset Auto-Add NetworkObject", false, 1)]
-        private static void ResetMultiplayerToolsTipStatus()
-        {
-            if (EditorPrefs.HasKey(AutoAddNetworkObjectIfNoneExists))
-            {
-                EditorPrefs.SetBool(AutoAddNetworkObjectIfNoneExists, false);
-            }
-        }
     }
 }

Editor/NetworkManagerEditor.cs

@@ -1,8 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
+using Unity.Netcode.Editor.Configuration;
 using UnityEditor;
 using UnityEngine;
-using UnityEditorInternal;
 
 namespace Unity.Netcode.Editor
 {
@@ -14,7 +15,6 @@ namespace Unity.Netcode.Editor
     [CanEditMultipleObjects]
     public class NetworkManagerEditor : UnityEditor.Editor
     {
-        internal const string InstallMultiplayerToolsTipDismissedPlayerPrefKey = "Netcode_Tip_InstallMPTools_Dismissed";
         private static GUIStyle s_CenteredWordWrappedLabelStyle;
         private static GUIStyle s_HelpBoxStyle;
 
@@ -40,8 +40,7 @@ namespace Unity.Netcode.Editor
         private SerializedProperty m_NetworkIdRecycleDelayProperty;
         private SerializedProperty m_RpcHashSizeProperty;
         private SerializedProperty m_LoadSceneTimeOutProperty;
-
+        private SerializedProperty m_PrefabsList;
-        private ReorderableList m_NetworkPrefabsList;
 
         private NetworkManager m_NetworkManager;
         private bool m_Initialized;
@@ -106,7 +105,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-
+            m_PrefabsList = m_NetworkConfigProperty
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
 
             ReloadTransports();
         }
@@ -132,76 +133,9 @@ namespace Unity.Netcode.Editor
             m_NetworkIdRecycleDelayProperty = m_NetworkConfigProperty.FindPropertyRelative("NetworkIdRecycleDelay");
             m_RpcHashSizeProperty = m_NetworkConfigProperty.FindPropertyRelative("RpcHashSize");
             m_LoadSceneTimeOutProperty = m_NetworkConfigProperty.FindPropertyRelative("LoadSceneTimeOut");
-        }
+            m_PrefabsList = m_NetworkConfigProperty
-
+                .FindPropertyRelative(nameof(NetworkConfig.Prefabs))
-        private void OnEnable()
+                .FindPropertyRelative(nameof(NetworkPrefabs.NetworkPrefabsLists));
-        {
-            m_NetworkPrefabsList = new ReorderableList(serializedObject, serializedObject.FindProperty(nameof(NetworkManager.NetworkConfig)).FindPropertyRelative(nameof(NetworkConfig.NetworkPrefabs)), true, true, true, true);
-            m_NetworkPrefabsList.elementHeightCallback = index =>
-            {
-                var networkOverrideInt = 0;
-                if (m_NetworkPrefabsList.count > 0)
-                {
-                    var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                    var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                    networkOverrideInt = networkOverrideProp.enumValueIndex;
-                }
-
-                return 8 + (networkOverrideInt == 0 ? EditorGUIUtility.singleLineHeight : (EditorGUIUtility.singleLineHeight * 2) + 5);
-            };
-            m_NetworkPrefabsList.drawElementCallback = (rect, index, isActive, isFocused) =>
-            {
-                rect.y += 5;
-
-                var networkPrefab = m_NetworkPrefabsList.serializedProperty.GetArrayElementAtIndex(index);
-                var networkPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Prefab));
-                var networkSourceHashProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourceHashToOverride));
-                var networkSourcePrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.SourcePrefabToOverride));
-                var networkTargetPrefabProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.OverridingTargetPrefab));
-                var networkOverrideProp = networkPrefab.FindPropertyRelative(nameof(NetworkPrefab.Override));
-                var networkOverrideInt = networkOverrideProp.enumValueIndex;
-                var networkOverrideEnum = (NetworkPrefabOverride)networkOverrideInt;
-                EditorGUI.LabelField(new Rect(rect.x + rect.width - 70, rect.y, 60, EditorGUIUtility.singleLineHeight), "Override");
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    if (EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), false))
-                    {
-                        networkOverrideProp.enumValueIndex = (int)NetworkPrefabOverride.Prefab;
-                    }
-                }
-                else
-                {
-                    if (!EditorGUI.Toggle(new Rect(rect.x + rect.width - 15, rect.y, 10, EditorGUIUtility.singleLineHeight), true))
-                    {
-                        networkOverrideProp.enumValueIndex = 0;
-                        networkOverrideEnum = NetworkPrefabOverride.None;
-                    }
-                }
-
-                if (networkOverrideEnum == NetworkPrefabOverride.None)
-                {
-                    EditorGUI.PropertyField(new Rect(rect.x, rect.y, rect.width - 80, EditorGUIUtility.singleLineHeight), networkPrefabProp, GUIContent.none);
-                }
-                else
-                {
-                    networkOverrideProp.enumValueIndex = GUI.Toolbar(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), networkOverrideInt - 1, new[] { "Prefab", "Hash" }) + 1;
-
-                    if (networkOverrideEnum == NetworkPrefabOverride.Prefab)
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourcePrefabProp, GUIContent.none);
-                    }
-                    else
-                    {
-                        EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 190, EditorGUIUtility.singleLineHeight), networkSourceHashProp, GUIContent.none);
-                    }
-
-                    rect.y += EditorGUIUtility.singleLineHeight + 5;
-
-                    EditorGUI.LabelField(new Rect(rect.x, rect.y, 100, EditorGUIUtility.singleLineHeight), "Overriding Prefab");
-                    EditorGUI.PropertyField(new Rect(rect.x + 110, rect.y, rect.width - 110, EditorGUIUtility.singleLineHeight), networkTargetPrefabProp, GUIContent.none);
-                }
-            };
-            m_NetworkPrefabsList.drawHeaderCallback = rect => EditorGUI.LabelField(rect, "NetworkPrefabs");
         }
 
         /// <inheritdoc/>
@@ -214,18 +148,6 @@ namespace Unity.Netcode.Editor
             DrawInstallMultiplayerToolsTip();
 #endif
 
-            {
-                var iterator = serializedObject.GetIterator();
-
-                for (bool enterChildren = true; iterator.NextVisible(enterChildren); enterChildren = false)
-                {
-                    using (new EditorGUI.DisabledScope("m_Script" == iterator.propertyPath))
-                    {
-                        EditorGUILayout.PropertyField(iterator, false);
-                    }
-                }
-            }
-
             if (!m_NetworkManager.IsServer && !m_NetworkManager.IsClient)
             {
                 serializedObject.Update();
@@ -236,7 +158,62 @@ namespace Unity.Netcode.Editor
                 EditorGUILayout.PropertyField(m_PlayerPrefabProperty);
                 EditorGUILayout.Space();
 
-                m_NetworkPrefabsList.DoLayoutList();
+                if (m_NetworkManager.NetworkConfig.HasOldPrefabList())
+                {
+                    EditorGUILayout.HelpBox("Network Prefabs serialized in old format. Migrate to new format to edit the list.", MessageType.Info);
+                    if (GUILayout.Button(new GUIContent("Migrate Prefab List", "Converts the old format Network Prefab list to a new Scriptable Object")))
+                    {
+                        // Default directory
+                        var directory = "Assets/";
+                        var assetPath = AssetDatabase.GetAssetPath(m_NetworkManager);
+                        if (assetPath == "")
+                        {
+                            assetPath = PrefabUtility.GetPrefabAssetPathOfNearestInstanceRoot(m_NetworkManager);
+                        }
+
+                        if (assetPath != "")
+                        {
+                            directory = Path.GetDirectoryName(assetPath);
+                        }
+                        else
+                        {
+#if UNITY_2021_1_OR_NEWER
+                            var prefabStage = UnityEditor.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#else
+                            var prefabStage = UnityEditor.Experimental.SceneManagement.PrefabStageUtility.GetPrefabStage(m_NetworkManager.gameObject);
+#endif
+                            if (prefabStage != null)
+                            {
+                                var prefabPath = prefabStage.assetPath;
+                                if (!string.IsNullOrEmpty(prefabPath))
+                                {
+                                    directory = Path.GetDirectoryName(prefabPath);
+                                }
+                            }
+                            if (m_NetworkManager.gameObject.scene != null)
+                            {
+                                var scenePath = m_NetworkManager.gameObject.scene.path;
+                                if (!string.IsNullOrEmpty(scenePath))
+                                {
+                                    directory = Path.GetDirectoryName(scenePath);
+                                }
+                            }
+                        }
+                        var networkPrefabs = m_NetworkManager.NetworkConfig.MigrateOldNetworkPrefabsToNetworkPrefabsList();
+                        string path = Path.Combine(directory, $"NetworkPrefabs-{m_NetworkManager.GetInstanceID()}.asset");
+                        Debug.Log("Saving migrated Network Prefabs List to " + path);
+                        AssetDatabase.CreateAsset(networkPrefabs, path);
+                        EditorUtility.SetDirty(m_NetworkManager);
+                    }
+                }
+                else
+                {
+                    if (m_NetworkManager.NetworkConfig.Prefabs.NetworkPrefabsLists.Count == 0)
+                    {
+                        EditorGUILayout.HelpBox("You have no prefab list selected. You will have to add your prefabs manually at runtime for netcode to work.", MessageType.Warning);
+                    }
+                    EditorGUILayout.PropertyField(m_PrefabsList);
+                }
                 EditorGUILayout.Space();
 
                 EditorGUILayout.LabelField("General", EditorStyles.boldLabel);
@@ -254,13 +231,7 @@ namespace Unity.Netcode.Editor
                     {
                         ReloadTransports();
 
-                        var transportComponent = m_NetworkManager.gameObject.GetComponent(m_TransportTypes[selection - 1]);
+                        var transportComponent = m_NetworkManager.gameObject.GetComponent(m_TransportTypes[selection - 1]) ?? m_NetworkManager.gameObject.AddComponent(m_TransportTypes[selection - 1]);
-
-                        if (transportComponent == null)
-                        {
-                            transportComponent = m_NetworkManager.gameObject.AddComponent(m_TransportTypes[selection - 1]);
-                        }
-
                         m_NetworkTransportProperty.objectReferenceValue = transportComponent;
 
                         Repaint();
@@ -371,22 +342,26 @@ namespace Unity.Netcode.Editor
             const string targetUrl = "https://docs-multiplayer.unity3d.com/netcode/current/tools/install-tools";
             const string infoIconName = "console.infoicon";
 
-            if (PlayerPrefs.GetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 0) != 0)
+            if (NetcodeForGameObjectsEditorSettings.GetNetcodeInstallMultiplayerToolTips() != 0)
             {
                 return;
             }
 
             if (s_CenteredWordWrappedLabelStyle == null)
             {
-                s_CenteredWordWrappedLabelStyle = new GUIStyle(GUI.skin.label);
+                s_CenteredWordWrappedLabelStyle = new GUIStyle(GUI.skin.label)
-                s_CenteredWordWrappedLabelStyle.wordWrap = true;
+                {
-                s_CenteredWordWrappedLabelStyle.alignment = TextAnchor.MiddleLeft;
+                    wordWrap = true,
+                    alignment = TextAnchor.MiddleLeft
+                };
             }
 
             if (s_HelpBoxStyle == null)
             {
-                s_HelpBoxStyle = new GUIStyle(EditorStyles.helpBox);
+                s_HelpBoxStyle = new GUIStyle(EditorStyles.helpBox)
-                s_HelpBoxStyle.padding = new RectOffset(10, 10, 10, 10);
+                {
+                    padding = new RectOffset(10, 10, 10, 10)
+                };
             }
 
             var openDocsButtonStyle = GUI.skin.button;
@@ -417,7 +392,7 @@ namespace Unity.Netcode.Editor
                 GUILayout.FlexibleSpace();
                 if (GUILayout.Button(dismissButtonText, dismissButtonStyle, GUILayout.ExpandWidth(false)))
                 {
-                    PlayerPrefs.SetInt(InstallMultiplayerToolsTipDismissedPlayerPrefKey, 1);
+                    NetcodeForGameObjectsEditorSettings.SetNetcodeInstallMultiplayerToolTips(1);
                 }
                 EditorGUIUtility.AddCursorRect(GUILayoutUtility.GetLastRect(), MouseCursor.Link);
                 GUILayout.FlexibleSpace();

Editor/NetworkManagerHelper.cs

@@ -1,8 +1,9 @@
 using System.Collections.Generic;
 using System.Linq;
+using Unity.Netcode.Editor.Configuration;
+using UnityEditor;
 using UnityEngine;
 using UnityEngine.SceneManagement;
-using UnityEditor;
 
 namespace Unity.Netcode.Editor
 {
@@ -32,6 +33,24 @@ namespace Unity.Netcode.Editor
 
             EditorApplication.playModeStateChanged += EditorApplication_playModeStateChanged;
             EditorApplication.hierarchyChanged += EditorApplication_hierarchyChanged;
+
+            // Initialize default values for new NetworkManagers
+            //
+            // When the default prefab list is enabled, this will default
+            // new NetworkManagers to using it.
+            //
+            // This will get run when new NetworkManagers are added, and
+            // when the user presses the "reset" button on a NetworkManager
+            // in the inspector.
+            NetworkManager.OnNetworkManagerReset = manager =>
+            {
+                var settings = NetcodeForGameObjectsProjectSettings.instance;
+                if (settings.GenerateDefaultNetworkPrefabs)
+                {
+                    manager.NetworkConfig = new NetworkConfig();
+                    manager.NetworkConfig.Prefabs.NetworkPrefabsLists = new List<NetworkPrefabsList> { NetworkPrefabProcessor.GetOrCreateNetworkPrefabs(NetworkPrefabProcessor.DefaultNetworkPrefabsPath, out _, true) };
+                }
+            };
         }
 
         private static void EditorApplication_playModeStateChanged(PlayModeStateChange playModeStateChange)
@@ -64,8 +83,12 @@ namespace Unity.Netcode.Editor
         {
             var scenesList = EditorBuildSettings.scenes.ToList();
             var activeScene = SceneManager.GetActiveScene();
-            var isSceneInBuildSettings = scenesList.Where((c) => c.path == activeScene.path).Count() == 1;
+            var isSceneInBuildSettings = scenesList.Count((c) => c.path == activeScene.path) == 1;
+#if UNITY_2023_1_OR_NEWER
+            var networkManager = Object.FindFirstObjectByType<NetworkManager>();
+#else
             var networkManager = Object.FindObjectOfType<NetworkManager>();
+#endif
             if (!isSceneInBuildSettings && networkManager != null)
             {
                 if (networkManager.NetworkConfig != null && networkManager.NetworkConfig.EnableSceneManagement)
@@ -109,9 +132,8 @@ namespace Unity.Netcode.Editor
         public void CheckAndNotifyUserNetworkObjectRemoved(NetworkManager networkManager, bool editorTest = false)
         {
             // Check for any NetworkObject at the same gameObject relative layer
-            var networkObject = networkManager.gameObject.GetComponent<NetworkObject>();
 
-            if (networkObject == null)
+            if (!networkManager.gameObject.TryGetComponent<NetworkObject>(out var networkObject))
             {
                 // if none is found, check to see if any children have a NetworkObject
                 networkObject = networkManager.gameObject.GetComponentInChildren<NetworkObject>();

Editor/NetworkObjectEditor.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
-using UnityEngine;
 using UnityEditor;
+using UnityEngine;
 
 namespace Unity.Netcode.Editor
 {
@@ -15,6 +15,8 @@ namespace Unity.Netcode.Editor
         private NetworkObject m_NetworkObject;
         private bool m_ShowObservers;
 
+        private static readonly string[] k_HiddenFields = { "m_Script" };
+
         private void Initialize()
         {
             if (m_Initialized)
@@ -95,7 +97,11 @@ namespace Unity.Netcode.Editor
             }
             else
             {
-                base.OnInspectorGUI();
+                EditorGUI.BeginChangeCheck();
+                serializedObject.UpdateIfRequiredOrScript();
+                DrawPropertiesExcluding(serializedObject, k_HiddenFields);
+                serializedObject.ApplyModifiedProperties();
+                EditorGUI.EndChangeCheck();
 
                 var guiEnabled = GUI.enabled;
                 GUI.enabled = false;

Editor/NetworkTransformEditor.cs

@@ -1,6 +1,6 @@
+using Unity.Netcode.Components;
 using UnityEditor;
 using UnityEngine;
-using Unity.Netcode.Components;
 
 namespace Unity.Netcode.Editor
 {
@@ -25,6 +25,11 @@ namespace Unity.Netcode.Editor
         private SerializedProperty m_InLocalSpaceProperty;
         private SerializedProperty m_InterpolateProperty;
 
+        private SerializedProperty m_UseQuaternionSynchronization;
+        private SerializedProperty m_UseQuaternionCompression;
+        private SerializedProperty m_UseHalfFloatPrecision;
+        private SerializedProperty m_SlerpPosition;
+
         private static int s_ToggleOffset = 45;
         private static float s_MaxRowWidth = EditorGUIUtility.labelWidth + EditorGUIUtility.fieldWidth + 5;
         private static GUIContent s_PositionLabel = EditorGUIUtility.TrTextContent("Position");
@@ -48,6 +53,10 @@ namespace Unity.Netcode.Editor
             m_ScaleThresholdProperty = serializedObject.FindProperty(nameof(NetworkTransform.ScaleThreshold));
             m_InLocalSpaceProperty = serializedObject.FindProperty(nameof(NetworkTransform.InLocalSpace));
             m_InterpolateProperty = serializedObject.FindProperty(nameof(NetworkTransform.Interpolate));
+            m_UseQuaternionSynchronization = serializedObject.FindProperty(nameof(NetworkTransform.UseQuaternionSynchronization));
+            m_UseQuaternionCompression = serializedObject.FindProperty(nameof(NetworkTransform.UseQuaternionCompression));
+            m_UseHalfFloatPrecision = serializedObject.FindProperty(nameof(NetworkTransform.UseHalfFloatPrecision));
+            m_SlerpPosition = serializedObject.FindProperty(nameof(NetworkTransform.SlerpPosition));
         }
 
         /// <inheritdoc/>
@@ -71,6 +80,8 @@ namespace Unity.Netcode.Editor
 
                 GUILayout.EndHorizontal();
             }
+
+            if (!m_UseQuaternionSynchronization.boolValue)
             {
                 GUILayout.BeginHorizontal();
 
@@ -88,6 +99,13 @@ namespace Unity.Netcode.Editor
 
                 GUILayout.EndHorizontal();
             }
+            else
+            {
+                m_SyncRotationXProperty.boolValue = true;
+                m_SyncRotationYProperty.boolValue = true;
+                m_SyncRotationZProperty.boolValue = true;
+            }
+
             {
                 GUILayout.BeginHorizontal();
 
@@ -116,6 +134,17 @@ namespace Unity.Netcode.Editor
             EditorGUILayout.LabelField("Configurations", EditorStyles.boldLabel);
             EditorGUILayout.PropertyField(m_InLocalSpaceProperty);
             EditorGUILayout.PropertyField(m_InterpolateProperty);
+            EditorGUILayout.PropertyField(m_SlerpPosition);
+            EditorGUILayout.PropertyField(m_UseQuaternionSynchronization);
+            if (m_UseQuaternionSynchronization.boolValue)
+            {
+                EditorGUILayout.PropertyField(m_UseQuaternionCompression);
+            }
+            else
+            {
+                m_UseQuaternionCompression.boolValue = false;
+            }
+            EditorGUILayout.PropertyField(m_UseHalfFloatPrecision);
 
 #if COM_UNITY_MODULES_PHYSICS
             // if rigidbody is present but network rigidbody is not present

Editor/com.unity.netcode.editor.asmdef

@@ -13,6 +13,26 @@
             "name": "com.unity.multiplayer.tools",
             "expression": "",
             "define": "MULTIPLAYER_TOOLS"
+        },
+        {
+            "name": "Unity",
+            "expression": "(0,2022.2.0a5)",
+            "define": "UNITY_UNET_PRESENT"
+        },
+        {
+            "name": "com.unity.modules.animation",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_ANIMATION"
+        },
+        {
+            "name": "com.unity.modules.physics",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_PHYSICS"
+        },
+        {
+            "name": "com.unity.modules.physics2d",
+            "expression": "",
+            "define": "COM_UNITY_MODULES_PHYSICS2D"
         }
     ]
 }

README.md

@@ -9,7 +9,7 @@ Netcode for GameObjects is a Unity package that provides networking capabilities
 
 Visit the [Multiplayer Docs Site](https://docs-multiplayer.unity3d.com/) for package & API documentation, as well as information about several samples which leverage the Netcode for GameObjects package.
 
-You can also jump right into our [Hello World](https://docs-multiplayer.unity3d.com/netcode/current/tutorials/helloworld/helloworldintro) guide for a taste of how to use the framework for basic networked tasks.
+You can also jump right into our [Hello World](https://docs-multiplayer.unity3d.com/netcode/current/tutorials/helloworld) guide for a taste of how to use the framework for basic networked tasks.
 
 ### Community and Feedback
 

Runtime/AssemblyInfo.cs

@@ -1,14 +1,25 @@
 using System.Runtime.CompilerServices;
-
+[assembly: InternalsVisibleTo("Unity.Netcode.Components")]
 #if UNITY_EDITOR
-[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor")]
-[assembly: InternalsVisibleTo("TestProject.EditorTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.Editor.CodeGen")]
-#endif
+#endif // UNITY_EDITOR
-[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#if MULTIPLAYER_TOOLS
-[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+[assembly: InternalsVisibleTo("Unity.Multiplayer.Tools.Adapters.Ngo1WithUtp2")]
+#endif // MULTIPLAYER_TOOLS
+#if COM_UNITY_NETCODE_ADAPTER_UTP
+[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+#endif // COM_UNITY_NETCODE_ADAPTER_UTP
+
+#if UNITY_INCLUDE_TESTS
 [assembly: InternalsVisibleTo("Unity.Netcode.RuntimeTests")]
 [assembly: InternalsVisibleTo("Unity.Netcode.TestHelpers.Runtime")]
-[assembly: InternalsVisibleTo("Unity.Netcode.Adapter.UTP")]
+[assembly: InternalsVisibleTo("TestProject.RuntimeTests")]
+#if UNITY_EDITOR
+[assembly: InternalsVisibleTo("Unity.Netcode.EditorTests")]
+[assembly: InternalsVisibleTo("TestProject.EditorTests")]
+#endif // UNITY_EDITOR
+#if MULTIPLAYER_TOOLS
+[assembly: InternalsVisibleTo("TestProject.ToolsIntegration.RuntimeTests")]
+#endif // MULTIPLAYER_TOOLS
+#endif // UNITY_INCLUDE_TESTS

Runtime/Configuration/NetworkConfig.cs

@@ -1,8 +1,9 @@
 using System;
 using System.Collections.Generic;
-using UnityEngine;
 using System.Linq;
 using Unity.Collections;
+using UnityEngine;
+using UnityEngine.Serialization;
 
 namespace Unity.Netcode
 {
@@ -30,20 +31,8 @@ namespace Unity.Netcode
         [Tooltip("When set, NetworkManager will automatically create and spawn the assigned player prefab. This can be overridden by adding it to the NetworkPrefabs list and selecting override.")]
         public GameObject PlayerPrefab;
 
-        /// <summary>
-        /// A list of prefabs that can be dynamically spawned.
-        /// </summary>
         [SerializeField]
-        [Tooltip("The prefabs that can be spawned across the network")]
+        public NetworkPrefabs Prefabs = new NetworkPrefabs();
-        internal List<NetworkPrefab> NetworkPrefabs = new List<NetworkPrefab>();
-
-        /// <summary>
-        /// This dictionary provides a quick way to check and see if a NetworkPrefab has a NetworkPrefab override.
-        /// Generated at runtime and OnValidate
-        /// </summary>
-        internal Dictionary<uint, NetworkPrefab> NetworkPrefabOverrideLinks = new Dictionary<uint, NetworkPrefab>();
-
-        internal Dictionary<uint, uint> OverrideToNetworkPrefab = new Dictionary<uint, uint>();
 
 
         /// <summary>
@@ -219,6 +208,14 @@ namespace Unity.Netcode
 
         private ulong? m_ConfigHash = null;
 
+        /// <summary>
+        /// Clears out the configuration hash value generated for a specific network session
+        /// </summary>
+        internal void ClearConfigHash()
+        {
+            m_ConfigHash = null;
+        }
+
         /// <summary>
         /// Gets a SHA256 hash of parts of the NetworkConfig instance
         /// </summary>
@@ -239,7 +236,7 @@ namespace Unity.Netcode
 
                 if (ForceSamePrefabs)
                 {
-                    var sortedDictionary = NetworkPrefabOverrideLinks.OrderBy(x => x.Key);
+                    var sortedDictionary = Prefabs.NetworkPrefabOverrideLinks.OrderBy(x => x.Key);
                     foreach (var sortedEntry in sortedDictionary)
 
                     {
@@ -273,6 +270,75 @@ namespace Unity.Netcode
         {
             return hash == GetConfig();
         }
+
+        internal void InitializePrefabs()
+        {
+            if (HasOldPrefabList())
+            {
+                MigrateOldNetworkPrefabsToNetworkPrefabsList();
+            }
+
+            Prefabs.Initialize();
+        }
+
+        [NonSerialized]
+        private bool m_DidWarnOldPrefabList = false;
+
+        private void WarnOldPrefabList()
+        {
+            if (!m_DidWarnOldPrefabList)
+            {
+                Debug.LogWarning("Using Legacy Network Prefab List. Consider Migrating.");
+                m_DidWarnOldPrefabList = true;
             }
         }
 
+        /// <summary>
+        /// Returns true if the old List&lt;NetworkPrefab&gt; serialized data is present.
+        /// </summary>
+        /// <remarks>
+        /// Internal use only to help migrate projects. <seealso cref="MigrateOldNetworkPrefabsToNetworkPrefabsList"/></remarks>
+        internal bool HasOldPrefabList()
+        {
+            return OldPrefabList?.Count > 0;
+        }
+
+        /// <summary>
+        /// Migrate the old format List&lt;NetworkPrefab&gt; prefab registration to the new NetworkPrefabsList ScriptableObject.
+        /// </summary>
+        /// <remarks>
+        /// OnAfterDeserialize cannot instantiate new objects (e.g. NetworkPrefabsList SO) since it executes in a thread, so we have to do it later.
+        /// Since NetworkConfig isn't a Unity.Object it doesn't get an Awake callback, so we have to do this in NetworkManager and expose this API.
+        /// </remarks>
+        internal NetworkPrefabsList MigrateOldNetworkPrefabsToNetworkPrefabsList()
+        {
+            if (OldPrefabList == null || OldPrefabList.Count == 0)
+            {
+                return null;
+            }
+
+            if (Prefabs == null)
+            {
+                throw new Exception("Prefabs field is null.");
+            }
+
+            Prefabs.NetworkPrefabsLists.Add(ScriptableObject.CreateInstance<NetworkPrefabsList>());
+
+            if (OldPrefabList?.Count > 0)
+            {
+                // Migrate legacy types/fields
+                foreach (var networkPrefab in OldPrefabList)
+                {
+                    Prefabs.NetworkPrefabsLists[Prefabs.NetworkPrefabsLists.Count - 1].Add(networkPrefab);
+                }
+            }
+
+            OldPrefabList = null;
+            return Prefabs.NetworkPrefabsLists[Prefabs.NetworkPrefabsLists.Count - 1];
+        }
+
+        [FormerlySerializedAs("NetworkPrefabs")]
+        [SerializeField]
+        internal List<NetworkPrefab> OldPrefabList;
+    }
+}

Runtime/Configuration/NetworkPrefab.cs

@@ -3,10 +3,23 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
-    internal enum NetworkPrefabOverride
+    /// <summary>
+    /// The method of NetworkPrefab override used to identify the source prefab
+    /// </summary>
+    public enum NetworkPrefabOverride
     {
+        /// <summary>
+        /// No oeverride is present
+        /// </summary>
         None,
+        /// <summary>
+        /// Override the prefab when the given SourcePrefabToOverride is requested
+        /// </summary>
         Prefab,
+        /// <summary>
+        /// Override the prefab when the given SourceHashToOverride is requested
+        /// Used in situations where the server assets do not exist in client builds
+        /// </summary>
         Hash
     }
 
@@ -14,10 +27,10 @@ namespace Unity.Netcode
     /// Class that represents a NetworkPrefab
     /// </summary>
     [Serializable]
-    internal class NetworkPrefab
+    public class NetworkPrefab
     {
         /// <summary>
-        /// The override setttings for this NetworkPrefab
+        /// The override settings for this NetworkPrefab
         /// </summary>
         public NetworkPrefabOverride Override;
 
@@ -41,5 +54,168 @@ namespace Unity.Netcode
         /// The prefab to replace (override) the source prefab with
         /// </summary>
         public GameObject OverridingTargetPrefab;
+
+        public bool Equals(NetworkPrefab other)
+        {
+            return Override == other.Override &&
+                   Prefab == other.Prefab &&
+                   SourcePrefabToOverride == other.SourcePrefabToOverride &&
+                   SourceHashToOverride == other.SourceHashToOverride &&
+                   OverridingTargetPrefab == other.OverridingTargetPrefab;
+        }
+
+        public uint SourcePrefabGlobalObjectIdHash
+        {
+            get
+            {
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.None:
+                        if (Prefab != null && Prefab.TryGetComponent(out NetworkObject no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Prefab field isn't set or isn't a Network Object");
+                    case NetworkPrefabOverride.Prefab:
+                        if (SourcePrefabToOverride != null && SourcePrefabToOverride.TryGetComponent(out no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Source Prefab field isn't set or isn't a Network Object");
+                    case NetworkPrefabOverride.Hash:
+                        return SourceHashToOverride;
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                }
+            }
+        }
+
+        public uint TargetPrefabGlobalObjectIdHash
+        {
+            get
+            {
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.None:
+                        return 0;
+                    case NetworkPrefabOverride.Prefab:
+                    case NetworkPrefabOverride.Hash:
+                        if (OverridingTargetPrefab != null && OverridingTargetPrefab.TryGetComponent(out NetworkObject no))
+                        {
+                            return no.GlobalObjectIdHash;
+                        }
+
+                        throw new InvalidOperationException("Target Prefab field isn't set or isn't a Network Object");
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                }
+            }
+        }
+
+        public bool Validate(int index = -1)
+        {
+            NetworkObject networkObject;
+            if (Override == NetworkPrefabOverride.None)
+            {
+                if (Prefab == null)
+                {
+                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} cannot be null ({nameof(NetworkPrefab)} at index: {index})");
+                    return false;
+                }
+
+                networkObject = Prefab.GetComponent<NetworkObject>();
+                if (networkObject == null)
+                {
+                    if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                    {
+                        NetworkLog.LogWarning($"{NetworkManager.PrefabDebugHelper(this)} is missing " +
+                                              $"a {nameof(NetworkObject)} component (entry will be ignored).");
+                    }
+                    return false;
+                }
+
+                return true;
+            }
+
+            // Validate source prefab override values first
+            switch (Override)
+            {
+                case NetworkPrefabOverride.Hash:
+                    {
+                        if (SourceHashToOverride == 0)
+                        {
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(SourceHashToOverride)} is zero " +
+                                    "(entry will be ignored).");
+                            }
+                            return false;
+                        }
+
+                        break;
+                    }
+                case NetworkPrefabOverride.Prefab:
+                    {
+                        if (SourcePrefabToOverride == null)
+                        {
+                            // This is a leftover side-effect from NetworkManager's OnValidate. It's a usability
+                            // adjustment to automatically set the "Prefab" field as the source prefab when a user
+                            // swaps from the default Inspector to the override one.
+                            if (Prefab != null)
+                            {
+                                SourcePrefabToOverride = Prefab;
+                            }
+                            else if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(SourcePrefabToOverride)} is null (entry will be ignored).");
+                                return false;
+                            }
+                        }
+
+                        if (!SourcePrefabToOverride.TryGetComponent(out networkObject))
+                        {
+                            if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                            {
+                                NetworkLog.LogWarning($"{nameof(NetworkPrefab)} ({SourcePrefabToOverride.name}) " +
+                                    $"is missing a {nameof(NetworkObject)} component (entry will be ignored).");
+                            }
+                            return false;
+                        }
+
+                        break;
+                    }
+            }
+
+            // Validate target prefab override values next
+            if (OverridingTargetPrefab == null)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                {
+                    NetworkLog.LogWarning($"{nameof(NetworkPrefab)} {nameof(OverridingTargetPrefab)} is null!");
+                }
+                switch (Override)
+                {
+                    case NetworkPrefabOverride.Hash:
+                        {
+                            Debug.LogWarning($"{nameof(NetworkPrefab)} override entry {SourceHashToOverride} will be removed and ignored.");
+                            break;
+                        }
+                    case NetworkPrefabOverride.Prefab:
+                        {
+                            Debug.LogWarning($"{nameof(NetworkPrefab)} override entry ({SourcePrefabToOverride.name}) will be removed and ignored.");
+                            break;
+                        }
+                }
+                return false;
+            }
+            return true;
+        }
+
+        public override string ToString()
+        {
+            return $"{{SourceHash: {SourceHashToOverride}, TargetHash: {TargetPrefabGlobalObjectIdHash}}}";
+        }
     }
 }

Runtime/Configuration/NetworkPrefabs.cs

@@ -0,0 +1,308 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using UnityEngine;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// A class that represents the runtime aspect of network prefabs.
+    /// This class contains processed prefabs from the NetworkPrefabsList, as
+    /// well as additional modifications (additions and removals) made at runtime.
+    /// </summary>
+    [Serializable]
+    public class NetworkPrefabs
+    {
+        /// <summary>
+        /// Edit-time scripted object containing a list of NetworkPrefabs.
+        /// </summary>
+        /// <remarks>
+        /// This field can be null if no prefabs are pre-configured.
+        /// Runtime usages of <see cref="NetworkPrefabs"/> should not depend on this edit-time field for execution.
+        /// </remarks>
+        [SerializeField]
+        public List<NetworkPrefabsList> NetworkPrefabsLists = new List<NetworkPrefabsList>();
+
+        /// <summary>
+        /// This dictionary provides a quick way to check and see if a NetworkPrefab has a NetworkPrefab override.
+        /// Generated at runtime and OnValidate
+        /// </summary>
+        [NonSerialized]
+        public Dictionary<uint, NetworkPrefab> NetworkPrefabOverrideLinks = new Dictionary<uint, NetworkPrefab>();
+
+        [NonSerialized]
+        public Dictionary<uint, uint> OverrideToNetworkPrefab = new Dictionary<uint, uint>();
+
+        public IReadOnlyList<NetworkPrefab> Prefabs => m_Prefabs;
+
+        [NonSerialized]
+        private List<NetworkPrefab> m_Prefabs = new List<NetworkPrefab>();
+
+        private void AddTriggeredByNetworkPrefabList(NetworkPrefab networkPrefab)
+        {
+            if (AddPrefabRegistration(networkPrefab))
+            {
+                m_Prefabs.Add(networkPrefab);
+            }
+        }
+
+        private void RemoveTriggeredByNetworkPrefabList(NetworkPrefab networkPrefab)
+        {
+            m_Prefabs.Remove(networkPrefab);
+        }
+
+        ~NetworkPrefabs()
+        {
+            Shutdown();
+        }
+
+        /// <summary>
+        /// Deregister from add and remove events
+        /// Clear the list
+        /// </summary>
+        internal void Shutdown()
+        {
+            foreach (var list in NetworkPrefabsLists)
+            {
+                list.OnAdd -= AddTriggeredByNetworkPrefabList;
+                list.OnRemove -= RemoveTriggeredByNetworkPrefabList;
+            }
+
+            NetworkPrefabsLists.Clear();
+        }
+
+        /// <summary>
+        /// Processes the <see cref="NetworkPrefabsList"/> if one is present for use during runtime execution,
+        /// else processes <see cref="Prefabs"/>.
+        /// </summary>
+        public void Initialize(bool warnInvalid = true)
+        {
+            if (NetworkPrefabsLists.Count != 0 && m_Prefabs.Count > 0)
+            {
+                NetworkLog.LogWarning("Runtime Network Prefabs was not empty at initialization time. Network " +
+                    "Prefab registrations made before initialization will be replaced by NetworkPrefabsList.");
+                m_Prefabs.Clear();
+            }
+
+            foreach (var list in NetworkPrefabsLists)
+            {
+                list.OnAdd += AddTriggeredByNetworkPrefabList;
+                list.OnRemove += RemoveTriggeredByNetworkPrefabList;
+            }
+
+            NetworkPrefabOverrideLinks.Clear();
+            OverrideToNetworkPrefab.Clear();
+
+            var prefabs = NetworkPrefabsLists.Count != 0 ? new List<NetworkPrefab>() : m_Prefabs;
+
+            if (NetworkPrefabsLists.Count != 0)
+            {
+                foreach (var list in NetworkPrefabsLists)
+                {
+                    foreach (var networkPrefab in list.PrefabList)
+                    {
+                        prefabs.Add(networkPrefab);
+                    }
+                }
+            }
+
+            m_Prefabs = new List<NetworkPrefab>();
+
+            List<NetworkPrefab> removeList = null;
+            if (warnInvalid)
+            {
+                removeList = new List<NetworkPrefab>();
+            }
+
+            foreach (var networkPrefab in prefabs)
+            {
+                if (AddPrefabRegistration(networkPrefab))
+                {
+                    m_Prefabs.Add(networkPrefab);
+                }
+                else
+                {
+                    removeList?.Add(networkPrefab);
+                }
+            }
+
+            // Clear out anything that is invalid or not used
+            if (removeList?.Count > 0)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Error)
+                {
+                    var sb = new StringBuilder("Removing invalid prefabs from Network Prefab registration: ");
+                    sb.Append(string.Join(", ", removeList));
+                    NetworkLog.LogWarning(sb.ToString());
+                }
+            }
+        }
+
+        /// <summary>
+        /// Add a new NetworkPrefab instance to the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public bool Add(NetworkPrefab networkPrefab)
+        {
+            if (AddPrefabRegistration(networkPrefab))
+            {
+                m_Prefabs.Add(networkPrefab);
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Remove a NetworkPrefab instance from the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public void Remove(NetworkPrefab prefab)
+        {
+            if (prefab == null)
+            {
+                throw new ArgumentNullException(nameof(prefab));
+            }
+
+            m_Prefabs.Remove(prefab);
+            OverrideToNetworkPrefab.Remove(prefab.TargetPrefabGlobalObjectIdHash);
+            NetworkPrefabOverrideLinks.Remove(prefab.SourcePrefabGlobalObjectIdHash);
+        }
+
+        /// <summary>
+        /// Remove a NetworkPrefab instance with matching <see cref="NetworkPrefab.Prefab"/> from the list
+        /// </summary>
+        /// <remarks>
+        /// The framework does not synchronize this list between clients. Any runtime changes must be handled manually.
+        ///
+        /// Any modifications made here are not persisted. Permanent configuration changes should be done
+        /// through the <see cref="NetworkPrefabsList"/> scriptable object property.
+        /// </remarks>
+        public void Remove(GameObject prefab)
+        {
+            if (prefab == null)
+            {
+                throw new ArgumentNullException(nameof(prefab));
+            }
+
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Prefab == prefab)
+                {
+                    Remove(m_Prefabs[i]);
+                    return;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Check if the given GameObject is present as a prefab within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(GameObject prefab)
+        {
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Prefab == prefab)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Check if the given NetworkPrefab is present within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(NetworkPrefab prefab)
+        {
+            for (int i = 0; i < m_Prefabs.Count; i++)
+            {
+                if (m_Prefabs[i].Equals(prefab))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Configures <see cref="NetworkPrefabOverrideLinks"/> and <see cref="OverrideToNetworkPrefab"/> for the given <see cref="NetworkPrefab"/>
+        /// </summary>
+        private bool AddPrefabRegistration(NetworkPrefab networkPrefab)
+        {
+            if (networkPrefab == null)
+            {
+                return false;
+            }
+            // Safeguard validation check since this method is called from outside of NetworkConfig and we can't control what's passed in.
+            if (!networkPrefab.Validate())
+            {
+                return false;
+            }
+
+            uint source = networkPrefab.SourcePrefabGlobalObjectIdHash;
+            uint target = networkPrefab.TargetPrefabGlobalObjectIdHash;
+
+            // Make sure the prefab isn't already registered.
+            if (NetworkPrefabOverrideLinks.ContainsKey(source))
+            {
+                var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
+
+                // This should never happen, but in the case it somehow does log an error and remove the duplicate entry
+                Debug.LogError($"{nameof(NetworkPrefab)} ({networkObject.name}) has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} source entry value of: {source}!");
+                return false;
+            }
+
+            // If we don't have an override configured, registration is simple!
+            if (networkPrefab.Override == NetworkPrefabOverride.None)
+            {
+                NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                return true;
+            }
+
+            // Make sure we don't have several overrides targeting the same prefab. Apparently we don't support that... shame.
+            if (OverrideToNetworkPrefab.ContainsKey(target))
+            {
+                var networkObject = networkPrefab.Prefab.GetComponent<NetworkObject>();
+
+                // This can happen if a user tries to make several GlobalObjectIdHash values point to the same target
+                Debug.LogError($"{nameof(NetworkPrefab)} (\"{networkObject.name}\") has a duplicate {nameof(NetworkObject.GlobalObjectIdHash)} target entry value of: {target}!");
+                return false;
+            }
+
+            switch (networkPrefab.Override)
+            {
+                case NetworkPrefabOverride.Prefab:
+                    {
+                        NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                        OverrideToNetworkPrefab.Add(target, source);
+                    }
+                    break;
+                case NetworkPrefabOverride.Hash:
+                    {
+                        NetworkPrefabOverrideLinks.Add(source, networkPrefab);
+                        OverrideToNetworkPrefab.Add(target, source);
+                    }
+                    break;
+            }
+
+            return true;
+        }
+    }
+}

Runtime/Configuration/NetworkPrefabs.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 230fc75f5639e46dc91734aa67d56a3e
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Configuration/NetworkPrefabsList.cs

@@ -0,0 +1,95 @@
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Serialization;
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// A ScriptableObject for holding a network prefabs list, which can be
+    /// shared between multiple NetworkManagers.
+    ///
+    /// When NetworkManagers hold references to this list, modifications to the
+    /// list at runtime will be picked up by all NetworkManagers that reference it.
+    /// </summary>
+    [CreateAssetMenu(fileName = "NetworkPrefabsList", menuName = "Netcode/Network Prefabs List")]
+    public class NetworkPrefabsList : ScriptableObject
+    {
+        internal delegate void OnAddDelegate(NetworkPrefab prefab);
+        internal OnAddDelegate OnAdd;
+
+        internal delegate void OnRemoveDelegate(NetworkPrefab prefab);
+        internal OnRemoveDelegate OnRemove;
+
+        [SerializeField]
+        internal bool IsDefault;
+
+        [FormerlySerializedAs("Prefabs")]
+        [SerializeField]
+        internal List<NetworkPrefab> List = new List<NetworkPrefab>();
+
+        /// <summary>
+        /// Read-only view into the prefabs list, enabling iterating and examining the list.
+        /// Actually modifying the list should be done using <see cref="Add"/>
+        /// and <see cref="Remove"/>.
+        /// </summary>
+        public IReadOnlyList<NetworkPrefab> PrefabList => List;
+
+        /// <summary>
+        /// Adds a prefab to the prefab list. Performing this here will apply the operation to all
+        /// <see cref="NetworkManager"/>s that reference this list.
+        /// </summary>
+        /// <param name="prefab"></param>
+        public void Add(NetworkPrefab prefab)
+        {
+            List.Add(prefab);
+            OnAdd?.Invoke(prefab);
+        }
+
+        /// <summary>
+        /// Removes a prefab from the prefab list. Performing this here will apply the operation to all
+        /// <see cref="NetworkManager"/>s that reference this list.
+        /// </summary>
+        /// <param name="prefab"></param>
+        public void Remove(NetworkPrefab prefab)
+        {
+            List.Remove(prefab);
+            OnRemove?.Invoke(prefab);
+        }
+
+        /// <summary>
+        /// Check if the given GameObject is present as a prefab within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(GameObject prefab)
+        {
+            for (int i = 0; i < List.Count; i++)
+            {
+                if (List[i].Prefab == prefab)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Check if the given NetworkPrefab is present within the list
+        /// </summary>
+        /// <param name="prefab">The prefab to check</param>
+        /// <returns>Whether or not the prefab exists</returns>
+        public bool Contains(NetworkPrefab prefab)
+        {
+            for (int i = 0; i < List.Count; i++)
+            {
+                if (List[i].Equals(prefab))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+    }
+}

Runtime/Configuration/NetworkPrefabsList.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: e651dbb3fbac04af2b8f5abf007ddc23
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Core/ComponentFactory.cs

@@ -52,6 +52,8 @@ namespace Unity.Netcode
         public static void SetDefaults()
         {
             SetDefault<IDeferredMessageManager>(networkManager => new DeferredMessageManager(networkManager));
+
+            SetDefault<IRealTimeProvider>(networkManager => new RealTimeProvider());
         }
 
         private static void SetDefault<T>(CreateObjectDelegate creator)

Runtime/Core/NetworkBehaviour.cs

@@ -1,9 +1,9 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using UnityEngine;
 using System.Reflection;
 using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -21,6 +21,7 @@ namespace Unity.Netcode
             Client = 2
         }
 
+
         // NetworkBehaviourILPP will override this in derived classes to return the name of the concrete type
         internal virtual string __getTypeName() => nameof(NetworkBehaviour);
 
@@ -81,7 +82,7 @@ namespace Unity.Netcode
                 var context = new NetworkContext
                 {
                     SenderId = NetworkManager.ServerClientId,
-                    Timestamp = Time.realtimeSinceStartup,
+                    Timestamp = NetworkManager.RealTimeProvider.RealTimeSinceStartup,
                     SystemOwner = NetworkManager,
                     // header information isn't valid since it's not a real message.
                     // RpcMessage doesn't access this stuff so it's just left empty.
@@ -218,7 +219,7 @@ namespace Unity.Netcode
                 var context = new NetworkContext
                 {
                     SenderId = NetworkManager.ServerClientId,
-                    Timestamp = Time.realtimeSinceStartup,
+                    Timestamp = NetworkManager.RealTimeProvider.RealTimeSinceStartup,
                     SystemOwner = NetworkManager,
                     // header information isn't valid since it's not a real message.
                     // RpcMessage doesn't access this stuff so it's just left empty.
@@ -235,16 +236,44 @@ namespace Unity.Netcode
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(rpcMethodId, out var rpcMethodName))
             {
-                foreach (var client in NetworkManager.ConnectedClients)
+                if (clientRpcParams.Send.TargetClientIds != null)
+                {
+                    foreach (var targetClientId in clientRpcParams.Send.TargetClientIds)
                     {
                         NetworkManager.NetworkMetrics.TrackRpcSent(
-                        client.Key,
+                            targetClientId,
                             NetworkObject,
                             rpcMethodName,
                             __getTypeName(),
                             rpcWriteSize);
                     }
                 }
+                else if (clientRpcParams.Send.TargetClientIdsNativeArray != null)
+                {
+                    foreach (var targetClientId in clientRpcParams.Send.TargetClientIdsNativeArray)
+                    {
+                        NetworkManager.NetworkMetrics.TrackRpcSent(
+                            targetClientId,
+                            NetworkObject,
+                            rpcMethodName,
+                            __getTypeName(),
+                            rpcWriteSize);
+                    }
+                }
+                else
+                {
+                    var observerEnumerator = NetworkObject.Observers.GetEnumerator();
+                    while (observerEnumerator.MoveNext())
+                    {
+                        NetworkManager.NetworkMetrics.TrackRpcSent(
+                            observerEnumerator.Current,
+                            NetworkObject,
+                            rpcMethodName,
+                            __getTypeName(),
+                            rpcWriteSize);
+                    }
+                }
+            }
 #endif
         }
 
@@ -258,7 +287,18 @@ namespace Unity.Netcode
         /// Gets the NetworkManager that owns this NetworkBehaviour instance
         ///   See note around `NetworkObject` for how there is a chicken / egg problem when we are not initialized
         /// </summary>
-        public NetworkManager NetworkManager => NetworkObject.NetworkManager;
+        public NetworkManager NetworkManager
+        {
+            get
+            {
+                if (NetworkObject?.NetworkManager != null)
+                {
+                    return NetworkObject?.NetworkManager;
+                }
+
+                return NetworkManager.Singleton;
+            }
+        }
 
         /// <summary>
         /// If a NetworkObject is assigned, it will return whether or not this NetworkObject
@@ -274,18 +314,18 @@ namespace Unity.Netcode
         /// <summary>
         /// Gets if we are executing as server
         /// </summary>
-        protected bool IsServer { get; private set; }
+        public bool IsServer { get; private set; }
 
         /// <summary>
         /// Gets if we are executing as client
         /// </summary>
-        protected bool IsClient { get; private set; }
+        public bool IsClient { get; private set; }
 
 
         /// <summary>
         /// Gets if we are executing as Host, I.E Server and Client
         /// </summary>
-        protected bool IsHost { get; private set; }
+        public bool IsHost { get; private set; }
 
         /// <summary>
         /// Gets Whether or not the object has a owner
@@ -307,31 +347,38 @@ namespace Unity.Netcode
                 m_NetworkObject.NetworkManager.IsServer;
         }
 
-        /// <summary>
-        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         ///  TODO: this needs an overhaul.  It's expensive, it's ja little naive in how it looks for networkObject in
         ///   its parent and worst, it creates a puzzle if you are a NetworkBehaviour wanting to see if you're live or not
         ///   (e.g. editor code).  All you want to do is find out if NetworkManager is null, but to do that you
         ///   need NetworkObject, but if you try and grab NetworkObject and NetworkManager isn't up you'll get
         ///   the warning below.  This is why IsBehaviourEditable had to be created.  Matt was going to re-do
         ///   how NetworkObject works but it was close to the release and too risky to change
-        ///
+        /// <summary>
+        /// Gets the NetworkObject that owns this NetworkBehaviour instance
         /// </summary>
         public NetworkObject NetworkObject
         {
             get
+            {
+                try
                 {
                     if (m_NetworkObject == null)
                     {
                         m_NetworkObject = GetComponentInParent<NetworkObject>();
                     }
+                }
+                catch (Exception)
+                {
+                    return null;
+                }
 
                 // ShutdownInProgress check:
                 // This prevents an edge case scenario where the NetworkManager is shutting down but user code
                 // in Update and/or in FixedUpdate could still be checking NetworkBehaviour.NetworkObject directly (i.e. does it exist?)
                 // or NetworkBehaviour.IsSpawned (i.e. to early exit if not spawned) which, in turn, could generate several Warning messages
                 // per spawned NetworkObject.  Checking for ShutdownInProgress prevents these unnecessary LogWarning messages.
-                if (m_NetworkObject == null && (NetworkManager.Singleton == null || !NetworkManager.Singleton.ShutdownInProgress))
+                // We must check IsSpawned, otherwise a warning will be logged under certain valid conditions (see OnDestroy)
+                if (IsSpawned && m_NetworkObject == null && (NetworkManager.Singleton == null || !NetworkManager.Singleton.ShutdownInProgress))
                 {
                     if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
                     {
@@ -435,15 +482,42 @@ namespace Unity.Netcode
             IsSpawned = true;
             InitializeVariables();
             UpdateNetworkProperties();
+        }
+
+        internal void VisibleOnNetworkSpawn()
+        {
+            try
+            {
                 OnNetworkSpawn();
             }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
+
+            InitializeVariables();
+            if (IsServer)
+            {
+                // Since we just spawned the object and since user code might have modified their NetworkVariable, esp.
+                // NetworkList, we need to mark the object as free of updates.
+                // This should happen for all objects on the machine triggering the spawn.
+                PostNetworkVariableWrite(true);
+            }
+        }
 
         internal void InternalOnNetworkDespawn()
         {
             IsSpawned = false;
             UpdateNetworkProperties();
+            try
+            {
                 OnNetworkDespawn();
             }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
+        }
 
         /// <summary>
         /// Gets called when the local client gains ownership of this object
@@ -496,13 +570,10 @@ namespace Unity.Netcode
             if (list == null)
             {
                 list = new List<FieldInfo>();
-                list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance));
-            }
-            else
-            {
-                list.AddRange(type.GetFields(BindingFlags.NonPublic | BindingFlags.Instance));
             }
 
+            list.AddRange(type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.DeclaredOnly));
+
             if (type.BaseType != null && type.BaseType != typeof(NetworkBehaviour))
             {
                 return GetFieldInfoForTypeRecursive(type.BaseType, list);
@@ -526,13 +597,7 @@ namespace Unity.Netcode
                 var fieldType = sortedFields[i].FieldType;
                 if (fieldType.IsSubclassOf(typeof(NetworkVariableBase)))
                 {
-                    var instance = (NetworkVariableBase)sortedFields[i].GetValue(this);
+                    var instance = (NetworkVariableBase)sortedFields[i].GetValue(this) ?? throw new Exception($"{GetType().FullName}.{sortedFields[i].Name} cannot be null. All {nameof(NetworkVariableBase)} instances must be initialized.");
-
-                    if (instance == null)
-                    {
-                        throw new Exception($"{GetType().FullName}.{sortedFields[i].Name} cannot be null. All {nameof(NetworkVariableBase)} instances must be initialized.");
-                    }
-
                     instance.Initialize(this);
 
                     var instanceNameProperty = fieldType.GetProperty(nameof(NetworkVariableBase.Name));
@@ -575,7 +640,18 @@ namespace Unity.Netcode
             NetworkVariableIndexesToResetSet.Clear();
         }
 
-        internal void PostNetworkVariableWrite()
+        internal void PostNetworkVariableWrite(bool forced = false)
+        {
+            if (forced)
+            {
+                // Mark every variable as no longer dirty. We just spawned the object and whatever the game code did
+                // during OnNetworkSpawn has been sent and needs to be cleared
+                for (int i = 0; i < NetworkVariableFields.Count; i++)
+                {
+                    NetworkVariableFields[i].ResetDirty();
+                }
+            }
+            else
             {
                 // mark any variables we wrote as no longer dirty
                 for (int i = 0; i < NetworkVariableIndexesToReset.Count; i++)
@@ -584,7 +660,10 @@ namespace Unity.Netcode
                 }
             }
 
-        internal void VariableUpdate(ulong targetClientId)
+            MarkVariablesDirty(false);
+        }
+
+        internal void PreVariableUpdate()
         {
             if (!m_VarInit)
             {
@@ -592,6 +671,10 @@ namespace Unity.Netcode
             }
 
             PreNetworkVariableWrite();
+        }
+
+        internal void VariableUpdate(ulong targetClientId)
+        {
             NetworkVariableUpdate(targetClientId, NetworkBehaviourId);
         }
 
@@ -638,7 +721,7 @@ namespace Unity.Netcode
                         var tmpWriter = new FastBufferWriter(MessagingSystem.NON_FRAGMENTED_MESSAGE_MAX_SIZE, Allocator.Temp, MessagingSystem.FRAGMENTED_MESSAGE_MAX_SIZE);
                         using (tmpWriter)
                         {
-                            message.Serialize(tmpWriter);
+                            message.Serialize(tmpWriter, message.Version);
                         }
                     }
                     else
@@ -663,14 +746,22 @@ namespace Unity.Netcode
             return false;
         }
 
-        internal void MarkVariablesDirty()
+        internal void MarkVariablesDirty(bool dirty)
         {
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                NetworkVariableFields[j].SetDirty(true);
+                NetworkVariableFields[j].SetDirty(dirty);
             }
         }
 
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
         internal void WriteNetworkVariableData(FastBufferWriter writer, ulong targetClientId)
         {
             if (NetworkVariableFields.Count == 0)
@@ -680,11 +771,17 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                bool canClientRead = NetworkVariableFields[j].CanClientRead(targetClientId);
 
-                if (canClientRead)
+                if (NetworkVariableFields[j].CanClientRead(targetClientId))
+                {
+                    if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
                         var writePos = writer.Position;
+                        // Note: This value can't be packed because we don't know how large it will be in advance
+                        // we reserve space for it, then write the data, then come back and fill in the space
+                        // to pack here, we'd have to write data to a temporary buffer and copy it in - which
+                        // isn't worth possibly saving one byte if and only if the data is less than 63 bytes long...
+                        // The way we do packing, any value > 63 in a ushort will use the full 2 bytes to represent.
                         writer.WriteValueSafe((ushort)0);
                         var startPos = writer.Position;
                         NetworkVariableFields[j].WriteField(writer);
@@ -694,13 +791,27 @@ namespace Unity.Netcode
                         writer.Seek(startPos + size);
                     }
                     else
+                    {
+                        NetworkVariableFields[j].WriteField(writer);
+                    }
+                }
+                else // Only if EnsureNetworkVariableLengthSafety, otherwise just skip
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     writer.WriteValueSafe((ushort)0);
                 }
             }
         }
 
-        internal void SetNetworkVariableData(FastBufferReader reader)
+        /// <summary>
+        /// Synchronizes by setting only the NetworkVariable field values that the client has permission to read.
+        /// Note: This is only invoked when first synchronizing a NetworkBehaviour (i.e. late join or spawned NetworkObject)
+        /// </summary>
+        /// <remarks>
+        /// When NetworkConfig.EnsureNetworkVariableLengthSafety is enabled each NetworkVariable field will be preceded
+        /// by the number of bytes written for that specific field.
+        /// </remarks>
+        internal void SetNetworkVariableData(FastBufferReader reader, ulong clientId)
         {
             if (NetworkVariableFields.Count == 0)
             {
@@ -709,13 +820,23 @@ namespace Unity.Netcode
 
             for (int j = 0; j < NetworkVariableFields.Count; j++)
             {
-                reader.ReadValueSafe(out ushort varSize);
+                var varSize = (ushort)0;
+                var readStartPos = 0;
+                if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
+                {
+                    reader.ReadValueSafe(out varSize);
                     if (varSize == 0)
                     {
                         continue;
                     }
+                    readStartPos = reader.Position;
+                }
+                else // If the client cannot read this field, then skip it
+                if (!NetworkVariableFields[j].CanClientRead(clientId))
+                {
+                    continue;
+                }
 
-                var readStartPos = reader.Position;
                 NetworkVariableFields[j].ReadField(reader);
 
                 if (NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
@@ -752,6 +873,156 @@ namespace Unity.Netcode
             return NetworkManager.SpawnManager.SpawnedObjects.TryGetValue(networkId, out NetworkObject networkObject) ? networkObject : null;
         }
 
+        /// <summary>
+        /// Override this method if your derived NetworkBehaviour requires custom synchronization data.
+        /// Note: Use of this method is only for the initial client synchronization of NetworkBehaviours
+        /// and will increase the payload size for client synchronization and dynamically spawned
+        /// <see cref="NetworkObject"/>s.
+        /// </summary>
+        /// <remarks>
+        /// When serializing (writing) this will be invoked during the client synchronization period and
+        /// when spawning new NetworkObjects.
+        /// When deserializing (reading), this will be invoked prior to the NetworkBehaviour's associated
+        /// NetworkObject being spawned.
+        /// </remarks>
+        /// <param name="serializer">The serializer to use to read and write the data.</param>
+        /// <typeparam name="T">
+        /// Either BufferSerializerReader or BufferSerializerWriter, depending whether the serializer
+        /// is in read mode or write mode.
+        /// </typeparam>
+        /// <param name="targetClientId">the relative client identifier being synchronized</param>
+        protected virtual void OnSynchronize<T>(ref BufferSerializer<T> serializer) where T : IReaderWriter
+        {
+
+        }
+
+        /// <summary>
+        /// The relative client identifier targeted for the serialization of this <see cref="NetworkBehaviour"/> instance.
+        /// </summary>
+        /// <remarks>
+        /// This value will be set prior to <see cref="OnSynchronize{T}(ref BufferSerializer{T})"/> being invoked.
+        /// For writing (server-side), this is useful to know which client will receive the serialized data.
+        /// For reading (client-side), this will be the <see cref="NetworkManager.LocalClientId"/>.
+        /// When synchronization of this instance is complete, this value will be reset to 0
+        /// </remarks>
+        protected ulong m_TargetIdBeingSynchronized { get; private set; }
+
+        /// <summary>
+        /// Internal method that determines if a NetworkBehaviour has additional synchronization data to
+        /// be synchronized when first instantiated prior to its associated NetworkObject being spawned.
+        /// </summary>
+        /// <remarks>
+        /// This includes try-catch blocks to recover from exceptions that might occur and continue to
+        /// synchronize any remaining NetworkBehaviours.
+        /// </remarks>
+        /// <returns>true if it wrote synchronization data and false if it did not</returns>
+        internal bool Synchronize<T>(ref BufferSerializer<T> serializer, ulong targetClientId = 0) where T : IReaderWriter
+        {
+            m_TargetIdBeingSynchronized = targetClientId;
+            if (serializer.IsWriter)
+            {
+                // Get the writer to handle seeking and determining how many bytes were written
+                var writer = serializer.GetFastBufferWriter();
+                // Save our position before we attempt to write anything so we can seek back to it (i.e. error occurs)
+                var positionBeforeWrite = writer.Position;
+                writer.WriteValueSafe(NetworkBehaviourId);
+
+                // Save our position where we will write the final size being written so we can skip over it in the
+                // event an exception occurs when deserializing.
+                var sizePosition = writer.Position;
+                writer.WriteValueSafe((ushort)0);
+
+                // Save our position before synchronizing to determine how much was written
+                var positionBeforeSynchronize = writer.Position;
+                var threwException = false;
+                try
+                {
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    threwException = true;
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization serialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                }
+                var finalPosition = writer.Position;
+
+                // Reset before exiting
+                m_TargetIdBeingSynchronized = default;
+                // If we wrote nothing then skip writing anything for this NetworkBehaviour
+                if (finalPosition == positionBeforeSynchronize || threwException)
+                {
+                    writer.Seek(positionBeforeWrite);
+                    return false;
+                }
+                else
+                {
+                    // Write the number of bytes serialized to handle exceptions on the deserialization side
+                    var bytesWritten = finalPosition - positionBeforeSynchronize;
+                    writer.Seek(sizePosition);
+                    writer.WriteValueSafe((ushort)bytesWritten);
+                    writer.Seek(finalPosition);
+                }
+                return true;
+            }
+            else
+            {
+                var reader = serializer.GetFastBufferReader();
+                // We will always read the expected byte count
+                reader.ReadValueSafe(out ushort expectedBytesToRead);
+
+                // Save our position before we begin synchronization deserialization
+                var positionBeforeSynchronize = reader.Position;
+                var synchronizationError = false;
+                try
+                {
+                    // Invoke synchronization
+                    OnSynchronize(ref serializer);
+                }
+                catch (Exception ex)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} threw an exception during synchronization deserialization, this {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                        if (NetworkManager.LogLevel == LogLevel.Developer)
+                        {
+                            NetworkLog.LogError($"{ex.Message}\n {ex.StackTrace}");
+                        }
+                    }
+                    synchronizationError = true;
+                }
+
+                var totalBytesRead = reader.Position - positionBeforeSynchronize;
+                if (totalBytesRead != expectedBytesToRead)
+                {
+                    if (NetworkManager.LogLevel <= LogLevel.Normal)
+                    {
+                        NetworkLog.LogWarning($"{name} read {totalBytesRead} bytes but was expected to read {expectedBytesToRead} bytes during synchronization deserialization! This {nameof(NetworkBehaviour)} is being skipped and will not be synchronized!");
+                    }
+                    synchronizationError = true;
+                }
+
+                // Reset before exiting
+                m_TargetIdBeingSynchronized = default;
+
+                // Skip over the entry if deserialization fails
+                if (synchronizationError)
+                {
+                    var skipToPosition = positionBeforeSynchronize + expectedBytesToRead;
+                    reader.Seek(skipToPosition);
+                    return false;
+                }
+                return true;
+            }
+        }
+
+
         /// <summary>
         /// Invoked when the <see cref="GameObject"/> the <see cref="NetworkBehaviour"/> is attached to.
         /// NOTE:  If you override this, you will want to always invoke this base class version of this
@@ -759,6 +1030,14 @@ namespace Unity.Netcode
         /// </summary>
         public virtual void OnDestroy()
         {
+            if (NetworkObject != null && NetworkObject.IsSpawned && IsSpawned)
+            {
+                // If the associated NetworkObject is still spawned then this
+                // NetworkBehaviour will be removed from the NetworkObject's
+                // ChildNetworkBehaviours list.
+                NetworkObject.OnNetworkBehaviourDestroyed(this);
+            }
+
             // this seems odd to do here, but in fact especially in tests we can find ourselves
             //  here without having called InitializedVariables, which causes problems if any
             //  of those variables use native containers (e.g. NetworkList) as they won't be
@@ -770,6 +1049,7 @@ namespace Unity.Netcode
                 InitializeVariables();
             }
 
+
             for (int i = 0; i < NetworkVariableFields.Count; i++)
             {
                 NetworkVariableFields[i].Dispose();

Runtime/Core/NetworkBehaviourUpdater.cs

@@ -8,12 +8,17 @@ namespace Unity.Netcode
     /// </summary>
     public class NetworkBehaviourUpdater
     {
-        private HashSet<NetworkObject> m_Touched = new HashSet<NetworkObject>();
+        private HashSet<NetworkObject> m_DirtyNetworkObjects = new HashSet<NetworkObject>();
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
         private ProfilerMarker m_NetworkBehaviourUpdate = new ProfilerMarker($"{nameof(NetworkBehaviour)}.{nameof(NetworkBehaviourUpdate)}");
 #endif
 
+        internal void AddForUpdate(NetworkObject networkObject)
+        {
+            m_DirtyNetworkObjects.Add(networkObject);
+        }
+
         internal void NetworkBehaviourUpdate(NetworkManager networkManager)
         {
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
@@ -21,59 +26,75 @@ namespace Unity.Netcode
 #endif
             try
             {
+                // NetworkObject references can become null, when hidden or despawned. Once NUll, there is no point
+                // trying to process them, even if they were previously marked as dirty.
+                m_DirtyNetworkObjects.RemoveWhere((sobj) => sobj == null);
+
                 if (networkManager.IsServer)
                 {
-                    m_Touched.Clear();
+                    foreach (var dirtyObj in m_DirtyNetworkObjects)
+                    {
+                        for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
+                        {
+                            dirtyObj.ChildNetworkBehaviours[k].PreVariableUpdate();
+                        }
+
                         for (int i = 0; i < networkManager.ConnectedClientsList.Count; i++)
                         {
                             var client = networkManager.ConnectedClientsList[i];
-                        var spawnedObjs = networkManager.SpawnManager.SpawnedObjectsList;
+
-                        m_Touched.UnionWith(spawnedObjs);
+                            if (dirtyObj.IsNetworkVisibleTo(client.ClientId))
-                        foreach (var sobj in spawnedObjs)
-                        {
-                            if (sobj.IsNetworkVisibleTo(client.ClientId))
                             {
                                 // Sync just the variables for just the objects this client sees
-                                for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                                for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
                                 {
-                                    sobj.ChildNetworkBehaviours[k].VariableUpdate(client.ClientId);
+                                    dirtyObj.ChildNetworkBehaviours[k].VariableUpdate(client.ClientId);
                                 }
                             }
                         }
                     }
-
-                    // Now, reset all the no-longer-dirty variables
-                    foreach (var sobj in m_Touched)
-                    {
-                        for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
-                        {
-                            sobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                        }
-                    }
                 }
                 else
                 {
                     // when client updates the server, it tells it about all its objects
-                    foreach (var sobj in networkManager.SpawnManager.SpawnedObjectsList)
+                    foreach (var sobj in m_DirtyNetworkObjects)
                     {
                         if (sobj.IsOwner)
                         {
+                            for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                            {
+                                sobj.ChildNetworkBehaviours[k].PreVariableUpdate();
+                            }
                             for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
                             {
                                 sobj.ChildNetworkBehaviours[k].VariableUpdate(NetworkManager.ServerClientId);
                             }
                         }
                     }
+                }
 
+                foreach (var dirtyObj in m_DirtyNetworkObjects)
+                {
+                    for (int k = 0; k < dirtyObj.ChildNetworkBehaviours.Count; k++)
+                    {
+                        var behaviour = dirtyObj.ChildNetworkBehaviours[k];
+                        for (int i = 0; i < behaviour.NetworkVariableFields.Count; i++)
+                        {
+                            if (behaviour.NetworkVariableFields[i].IsDirty() &&
+                                !behaviour.NetworkVariableIndexesToResetSet.Contains(i))
+                            {
+                                behaviour.NetworkVariableIndexesToResetSet.Add(i);
+                                behaviour.NetworkVariableIndexesToReset.Add(i);
+                            }
+                        }
+                    }
+                }
                 // Now, reset all the no-longer-dirty variables
-                    foreach (var sobj in networkManager.SpawnManager.SpawnedObjectsList)
+                foreach (var dirtyobj in m_DirtyNetworkObjects)
                 {
-                        for (int k = 0; k < sobj.ChildNetworkBehaviours.Count; k++)
+                    dirtyobj.PostNetworkVariableWrite();
-                        {
-                            sobj.ChildNetworkBehaviours[k].PostNetworkVariableWrite();
-                        }
-                    }
                 }
+                m_DirtyNetworkObjects.Clear();
             }
             finally
             {

Runtime/Core/NetworkUpdateLoop.cs

@@ -167,7 +167,7 @@ namespace Unity.Netcode
         /// </summary>
         public static NetworkUpdateStage UpdateStage;
 
-        private static void RunNetworkUpdateStage(NetworkUpdateStage updateStage)
+        internal static void RunNetworkUpdateStage(NetworkUpdateStage updateStage)
         {
             UpdateStage = updateStage;
 

Runtime/Hashing/XXHash.cs

@@ -0,0 +1,248 @@
+using System;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace Unity.Netcode
+{
+    internal static class XXHash
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe uint Hash32(byte* input, int length, uint seed = 0)
+        {
+            unchecked
+            {
+                const uint prime1 = 2654435761u;
+                const uint prime2 = 2246822519u;
+                const uint prime3 = 3266489917u;
+                const uint prime4 = 0668265263u;
+                const uint prime5 = 0374761393u;
+
+                uint hash = seed + prime5;
+
+                if (length >= 16)
+                {
+                    uint val0 = seed + prime1 + prime2;
+                    uint val1 = seed + prime2;
+                    uint val2 = seed + 0;
+                    uint val3 = seed - prime1;
+
+                    int count = length >> 4;
+                    for (int i = 0; i < count; i++)
+                    {
+                        var pos0 = *(uint*)(input + 0);
+                        var pos1 = *(uint*)(input + 4);
+                        var pos2 = *(uint*)(input + 8);
+                        var pos3 = *(uint*)(input + 12);
+
+                        val0 += pos0 * prime2;
+                        val0 = (val0 << 13) | (val0 >> (32 - 13));
+                        val0 *= prime1;
+
+                        val1 += pos1 * prime2;
+                        val1 = (val1 << 13) | (val1 >> (32 - 13));
+                        val1 *= prime1;
+
+                        val2 += pos2 * prime2;
+                        val2 = (val2 << 13) | (val2 >> (32 - 13));
+                        val2 *= prime1;
+
+                        val3 += pos3 * prime2;
+                        val3 = (val3 << 13) | (val3 >> (32 - 13));
+                        val3 *= prime1;
+
+                        input += 16;
+                    }
+
+                    hash = ((val0 << 01) | (val0 >> (32 - 01))) +
+                           ((val1 << 07) | (val1 >> (32 - 07))) +
+                           ((val2 << 12) | (val2 >> (32 - 12))) +
+                           ((val3 << 18) | (val3 >> (32 - 18)));
+                }
+
+                hash += (uint)length;
+
+                length &= 15;
+                while (length >= 4)
+                {
+                    hash += *(uint*)input * prime3;
+                    hash = ((hash << 17) | (hash >> (32 - 17))) * prime4;
+                    input += 4;
+                    length -= 4;
+                }
+                while (length > 0)
+                {
+                    hash += *input * prime5;
+                    hash = ((hash << 11) | (hash >> (32 - 11))) * prime1;
+                    ++input;
+                    --length;
+                }
+
+                hash ^= hash >> 15;
+                hash *= prime2;
+                hash ^= hash >> 13;
+                hash *= prime3;
+                hash ^= hash >> 16;
+
+                return hash;
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe ulong Hash64(byte* input, int length, uint seed = 0)
+        {
+            unchecked
+            {
+                const ulong prime1 = 11400714785074694791ul;
+                const ulong prime2 = 14029467366897019727ul;
+                const ulong prime3 = 01609587929392839161ul;
+                const ulong prime4 = 09650029242287828579ul;
+                const ulong prime5 = 02870177450012600261ul;
+
+                ulong hash = seed + prime5;
+
+                if (length >= 32)
+                {
+                    ulong val0 = seed + prime1 + prime2;
+                    ulong val1 = seed + prime2;
+                    ulong val2 = seed + 0;
+                    ulong val3 = seed - prime1;
+
+                    int count = length >> 5;
+                    for (int i = 0; i < count; i++)
+                    {
+                        var pos0 = *(ulong*)(input + 0);
+                        var pos1 = *(ulong*)(input + 8);
+                        var pos2 = *(ulong*)(input + 16);
+                        var pos3 = *(ulong*)(input + 24);
+
+                        val0 += pos0 * prime2;
+                        val0 = (val0 << 31) | (val0 >> (64 - 31));
+                        val0 *= prime1;
+
+                        val1 += pos1 * prime2;
+                        val1 = (val1 << 31) | (val1 >> (64 - 31));
+                        val1 *= prime1;
+
+                        val2 += pos2 * prime2;
+                        val2 = (val2 << 31) | (val2 >> (64 - 31));
+                        val2 *= prime1;
+
+                        val3 += pos3 * prime2;
+                        val3 = (val3 << 31) | (val3 >> (64 - 31));
+                        val3 *= prime1;
+
+                        input += 32;
+                    }
+
+                    hash = ((val0 << 01) | (val0 >> (64 - 01))) +
+                           ((val1 << 07) | (val1 >> (64 - 07))) +
+                           ((val2 << 12) | (val2 >> (64 - 12))) +
+                           ((val3 << 18) | (val3 >> (64 - 18)));
+
+                    val0 *= prime2;
+                    val0 = (val0 << 31) | (val0 >> (64 - 31));
+                    val0 *= prime1;
+                    hash ^= val0;
+                    hash = hash * prime1 + prime4;
+
+                    val1 *= prime2;
+                    val1 = (val1 << 31) | (val1 >> (64 - 31));
+                    val1 *= prime1;
+                    hash ^= val1;
+                    hash = hash * prime1 + prime4;
+
+                    val2 *= prime2;
+                    val2 = (val2 << 31) | (val2 >> (64 - 31));
+                    val2 *= prime1;
+                    hash ^= val2;
+                    hash = hash * prime1 + prime4;
+
+                    val3 *= prime2;
+                    val3 = (val3 << 31) | (val3 >> (64 - 31));
+                    val3 *= prime1;
+                    hash ^= val3;
+                    hash = hash * prime1 + prime4;
+                }
+
+                hash += (ulong)length;
+
+                length &= 31;
+                while (length >= 8)
+                {
+                    ulong lane = *(ulong*)input * prime2;
+                    lane = ((lane << 31) | (lane >> (64 - 31))) * prime1;
+                    hash ^= lane;
+                    hash = ((hash << 27) | (hash >> (64 - 27))) * prime1 + prime4;
+                    input += 8;
+                    length -= 8;
+                }
+                if (length >= 4)
+                {
+                    hash ^= *(uint*)input * prime1;
+                    hash = ((hash << 23) | (hash >> (64 - 23))) * prime2 + prime3;
+                    input += 4;
+                    length -= 4;
+                }
+                while (length > 0)
+                {
+                    hash ^= *input * prime5;
+                    hash = ((hash << 11) | (hash >> (64 - 11))) * prime1;
+                    ++input;
+                    --length;
+                }
+
+                hash ^= hash >> 33;
+                hash *= prime2;
+                hash ^= hash >> 29;
+                hash *= prime3;
+                hash ^= hash >> 32;
+
+                return hash;
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this byte[] buffer)
+        {
+            int length = buffer.Length;
+            unsafe
+            {
+                fixed (byte* pointer = buffer)
+                {
+                    return Hash32(pointer, length);
+                }
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this string text) => Hash32(Encoding.UTF8.GetBytes(text));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32(this Type type) => Hash32(type.FullName);
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static uint Hash32<T>() => Hash32(typeof(T));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this byte[] buffer)
+        {
+            int length = buffer.Length;
+            unsafe
+            {
+                fixed (byte* pointer = buffer)
+                {
+                    return Hash64(pointer, length);
+                }
+            }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this string text) => Hash64(Encoding.UTF8.GetBytes(text));
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64(this Type type) => Hash64(type.FullName);
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ulong Hash64<T>() => Hash64(typeof(T));
+    }
+}

Runtime/Hashing/XXHash.cs.meta

@@ -1,5 +1,5 @@
 fileFormatVersion: 2
-guid: b5aa7a49e9e694f148d810d34577546b
+guid: c3077af091aa443acbdea9d3e97727b0
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

Runtime/Hashing/XXHash.meta

@@ -1,8 +0,0 @@
-fileFormatVersion: 2
-guid: 2c61e8fe9a68a486fbbc3128d233ded2
-folderAsset: yes
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Hashing/XXHash/LICENSE

@@ -1,21 +0,0 @@
-The MIT License (MIT)
-
-Copyright (c) 2015, 2016 Sedat Kapanoglu
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.

Runtime/Hashing/XXHash/LICENSE.meta

@@ -1,7 +0,0 @@
-fileFormatVersion: 2
-guid: cf89ecbf6f9954c8ea6d0848b1e79d87
-DefaultImporter:
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Runtime/Hashing/XXHash/XXHash.cs

@@ -1,318 +0,0 @@
-// <copyright file="XXHash.cs" company="Sedat Kapanoglu">
-// Copyright (c) 2015-2019 Sedat Kapanoglu
-// MIT License (see LICENSE file for details)
-// </copyright>
-
-// @mfatihmar (Unity): Modified for Unity support
-
-using System.Text;
-using System.Runtime.CompilerServices;
-
-namespace Unity.Netcode
-{
-    /// <summary>
-    /// XXHash implementation.
-    /// </summary>
-    internal static class XXHash
-    {
-        private const ulong k_Prime64v1 = 11400714785074694791ul;
-        private const ulong k_Prime64v2 = 14029467366897019727ul;
-        private const ulong k_Prime64v3 = 1609587929392839161ul;
-        private const ulong k_Prime64v4 = 9650029242287828579ul;
-        private const ulong k_Prime64v5 = 2870177450012600261ul;
-
-        private const uint k_Prime32v1 = 2654435761u;
-        private const uint k_Prime32v2 = 2246822519u;
-        private const uint k_Prime32v3 = 3266489917u;
-        private const uint k_Prime32v4 = 668265263u;
-        private const uint k_Prime32v5 = 374761393u;
-
-        public static uint Hash32(string text) => Hash32(text, Encoding.UTF8);
-        public static uint Hash32(string text, Encoding encoding) => Hash32(encoding.GetBytes(text));
-        public static uint Hash32(byte[] buffer)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = buffer)
-                {
-                    return Hash32(ptr, buffer.Length);
-                }
-            }
-        }
-
-        /// <summary>
-        /// Generate a 32-bit xxHash value.
-        /// </summary>
-        /// <param name="buffer">Input buffer.</param>
-        /// <param name="bufferLength">Input buffer length.</param>
-        /// <param name="seed">Optional seed.</param>
-        /// <returns>32-bit hash value.</returns>
-        public static unsafe uint Hash32(byte* buffer, int bufferLength, uint seed = 0)
-        {
-            const int stripeLength = 16;
-
-            int len = bufferLength;
-            int remainingLen = len;
-            uint acc;
-
-            byte* pInput = buffer;
-            if (len >= stripeLength)
-            {
-                uint acc1 = seed + k_Prime32v1 + k_Prime32v2;
-                uint acc2 = seed + k_Prime32v2;
-                uint acc3 = seed;
-                uint acc4 = seed - k_Prime32v1;
-
-                do
-                {
-                    acc = processStripe32(ref pInput, ref acc1, ref acc2, ref acc3, ref acc4);
-                    remainingLen -= stripeLength;
-                } while (remainingLen >= stripeLength);
-            }
-            else
-            {
-                acc = seed + k_Prime32v5;
-            }
-
-            acc += (uint)len;
-            acc = processRemaining32(pInput, acc, remainingLen);
-
-            return avalanche32(acc);
-        }
-
-        public static ulong Hash64(string text) => Hash64(text, Encoding.UTF8);
-        public static ulong Hash64(string text, Encoding encoding) => Hash64(encoding.GetBytes(text));
-        public static ulong Hash64(byte[] buffer)
-        {
-            unsafe
-            {
-                fixed (byte* ptr = buffer)
-                {
-                    return Hash64(ptr, buffer.Length);
-                }
-            }
-        }
-
-        /// <summary>
-        /// Generate a 64-bit xxHash value.
-        /// </summary>
-        /// <param name="buffer">Input buffer.</param>
-        /// <param name="bufferLength">Input buffer length.</param>
-        /// <param name="seed">Optional seed.</param>
-        /// <returns>Computed 64-bit hash value.</returns>
-        public static unsafe ulong Hash64(byte* buffer, int bufferLength, ulong seed = 0)
-        {
-            const int stripeLength = 32;
-
-            int len = bufferLength;
-            int remainingLen = len;
-            ulong acc;
-
-            byte* pInput = buffer;
-            if (len >= stripeLength)
-            {
-                ulong acc1 = seed + k_Prime64v1 + k_Prime64v2;
-                ulong acc2 = seed + k_Prime64v2;
-                ulong acc3 = seed;
-                ulong acc4 = seed - k_Prime64v1;
-
-                do
-                {
-                    acc = processStripe64(ref pInput, ref acc1, ref acc2, ref acc3, ref acc4);
-                    remainingLen -= stripeLength;
-                } while (remainingLen >= stripeLength);
-            }
-            else
-            {
-                acc = seed + k_Prime64v5;
-            }
-
-            acc += (ulong)len;
-            acc = processRemaining64(pInput, acc, remainingLen);
-
-
-            return avalanche64(acc);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe ulong processStripe64(
-            ref byte* pInput,
-            ref ulong acc1,
-            ref ulong acc2,
-            ref ulong acc3,
-            ref ulong acc4)
-        {
-            processLane64(ref acc1, ref pInput);
-            processLane64(ref acc2, ref pInput);
-            processLane64(ref acc3, ref pInput);
-            processLane64(ref acc4, ref pInput);
-
-            ulong acc = Bits.RotateLeft(acc1, 1)
-                        + Bits.RotateLeft(acc2, 7)
-                        + Bits.RotateLeft(acc3, 12)
-                        + Bits.RotateLeft(acc4, 18);
-
-            mergeAccumulator64(ref acc, acc1);
-            mergeAccumulator64(ref acc, acc2);
-            mergeAccumulator64(ref acc, acc3);
-            mergeAccumulator64(ref acc, acc4);
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe void processLane64(ref ulong accn, ref byte* pInput)
-        {
-            ulong lane = *(ulong*)pInput;
-            accn = round64(accn, lane);
-            pInput += 8;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe ulong processRemaining64(
-            byte* pInput,
-            ulong acc,
-            int remainingLen)
-        {
-            for (ulong lane; remainingLen >= 8; remainingLen -= 8, pInput += 8)
-            {
-                lane = *(ulong*)pInput;
-
-                acc ^= round64(0, lane);
-                acc = Bits.RotateLeft(acc, 27) * k_Prime64v1;
-                acc += k_Prime64v4;
-            }
-
-            for (uint lane32; remainingLen >= 4; remainingLen -= 4, pInput += 4)
-            {
-                lane32 = *(uint*)pInput;
-
-                acc ^= lane32 * k_Prime64v1;
-                acc = Bits.RotateLeft(acc, 23) * k_Prime64v2;
-                acc += k_Prime64v3;
-            }
-
-            for (byte lane8; remainingLen >= 1; remainingLen--, pInput++)
-            {
-                lane8 = *pInput;
-                acc ^= lane8 * k_Prime64v5;
-                acc = Bits.RotateLeft(acc, 11) * k_Prime64v1;
-            }
-
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static ulong avalanche64(ulong acc)
-        {
-            acc ^= acc >> 33;
-            acc *= k_Prime64v2;
-            acc ^= acc >> 29;
-            acc *= k_Prime64v3;
-            acc ^= acc >> 32;
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static ulong round64(ulong accn, ulong lane)
-        {
-            accn += lane * k_Prime64v2;
-            return Bits.RotateLeft(accn, 31) * k_Prime64v1;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static void mergeAccumulator64(ref ulong acc, ulong accn)
-        {
-            acc ^= round64(0, accn);
-            acc *= k_Prime64v1;
-            acc += k_Prime64v4;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe uint processStripe32(
-            ref byte* pInput,
-            ref uint acc1,
-            ref uint acc2,
-            ref uint acc3,
-            ref uint acc4)
-        {
-            processLane32(ref pInput, ref acc1);
-            processLane32(ref pInput, ref acc2);
-            processLane32(ref pInput, ref acc3);
-            processLane32(ref pInput, ref acc4);
-
-            return Bits.RotateLeft(acc1, 1)
-                   + Bits.RotateLeft(acc2, 7)
-                   + Bits.RotateLeft(acc3, 12)
-                   + Bits.RotateLeft(acc4, 18);
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe void processLane32(ref byte* pInput, ref uint accn)
-        {
-            uint lane = *(uint*)pInput;
-            accn = round32(accn, lane);
-            pInput += 4;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe uint processRemaining32(
-            byte* pInput,
-            uint acc,
-            int remainingLen)
-        {
-            for (uint lane; remainingLen >= 4; remainingLen -= 4, pInput += 4)
-            {
-                lane = *(uint*)pInput;
-                acc += lane * k_Prime32v3;
-                acc = Bits.RotateLeft(acc, 17) * k_Prime32v4;
-            }
-
-            for (byte lane; remainingLen >= 1; remainingLen--, pInput++)
-            {
-                lane = *pInput;
-                acc += lane * k_Prime32v5;
-                acc = Bits.RotateLeft(acc, 11) * k_Prime32v1;
-            }
-
-            return acc;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static uint round32(uint accn, uint lane)
-        {
-            accn += lane * k_Prime32v2;
-            accn = Bits.RotateLeft(accn, 13);
-            accn *= k_Prime32v1;
-            return accn;
-        }
-
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static uint avalanche32(uint acc)
-        {
-            acc ^= acc >> 15;
-            acc *= k_Prime32v2;
-            acc ^= acc >> 13;
-            acc *= k_Prime32v3;
-            acc ^= acc >> 16;
-            return acc;
-        }
-
-        /// <summary>
-        /// Bit operations.
-        /// </summary>
-        private static class Bits
-        {
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            internal static ulong RotateLeft(ulong value, int bits)
-            {
-                return (value << bits) | (value >> (64 - bits));
-            }
-
-            [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            internal static uint RotateLeft(uint value, int bits)
-            {
-                return (value << bits) | (value >> (32 - bits));
-            }
-        }
-    }
-}

Runtime/Messaging/BatchHeader.cs

@@ -5,9 +5,26 @@ namespace Unity.Netcode
     /// </summary>
     internal struct BatchHeader : INetworkSerializeByMemcpy
     {
+        internal const ushort MagicValue = 0x1160;
+        /// <summary>
+        /// A magic number to detect corrupt messages.
+        /// Always set to k_MagicValue
+        /// </summary>
+        public ushort Magic;
+
+        /// <summary>
+        /// Total number of bytes in the batch.
+        /// </summary>
+        public int BatchSize;
+
+        /// <summary>
+        /// Hash of the message to detect corrupt messages.
+        /// </summary>
+        public ulong BatchHash;
+
         /// <summary>
         /// Total number of messages in the batch.
         /// </summary>
-        public ushort BatchSize;
+        public ushort BatchCount;
     }
 }

Runtime/Messaging/CustomMessageManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Unity.Collections;
 
 namespace Unity.Netcode
 {
@@ -68,9 +69,23 @@ namespace Unity.Netcode
 
             if (clientIds == null)
             {
-                throw new ArgumentNullException("You must pass in a valid clientId List");
+                throw new ArgumentNullException(nameof(clientIds), "You must pass in a valid clientId List");
             }
 
+            if (m_NetworkManager.IsHost)
+            {
+                for (var i = 0; i < clientIds.Count; ++i)
+                {
+                    if (clientIds[i] == m_NetworkManager.LocalClientId)
+                    {
+                        InvokeUnnamedMessage(
+                            m_NetworkManager.LocalClientId,
+                            new FastBufferReader(messageBuffer, Allocator.None),
+                            0
+                        );
+                    }
+                }
+            }
             var message = new UnnamedMessage
             {
                 SendData = messageBuffer
@@ -92,6 +107,18 @@ namespace Unity.Netcode
         /// <param name="networkDelivery">The delivery type (QoS) to send data with</param>
         public void SendUnnamedMessage(ulong clientId, FastBufferWriter messageBuffer, NetworkDelivery networkDelivery = NetworkDelivery.ReliableSequenced)
         {
+            if (m_NetworkManager.IsHost)
+            {
+                if (clientId == m_NetworkManager.LocalClientId)
+                {
+                    InvokeUnnamedMessage(
+                        m_NetworkManager.LocalClientId,
+                        new FastBufferReader(messageBuffer, Allocator.None),
+                        0
+                    );
+                    return;
+                }
+            }
             var message = new UnnamedMessage
             {
                 SendData = messageBuffer
@@ -124,14 +151,18 @@ namespace Unity.Netcode
                 // We dont know what size to use. Try every (more collision prone)
                 if (m_NamedMessageHandlers32.TryGetValue(hash, out HandleNamedMessageDelegate messageHandler32))
                 {
+                    // handler can remove itself, cache the name for metrics
+                    string messageName = m_MessageHandlerNameLookup32[hash];
                     messageHandler32(sender, reader);
-                    m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, m_MessageHandlerNameLookup32[hash], bytesCount);
+                    m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, messageName, bytesCount);
                 }
 
                 if (m_NamedMessageHandlers64.TryGetValue(hash, out HandleNamedMessageDelegate messageHandler64))
                 {
+                    // handler can remove itself, cache the name for metrics
+                    string messageName = m_MessageHandlerNameLookup64[hash];
                     messageHandler64(sender, reader);
-                    m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, m_MessageHandlerNameLookup64[hash], bytesCount);
+                    m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, messageName, bytesCount);
                 }
             }
             else
@@ -142,15 +173,19 @@ namespace Unity.Netcode
                     case HashSize.VarIntFourBytes:
                         if (m_NamedMessageHandlers32.TryGetValue(hash, out HandleNamedMessageDelegate messageHandler32))
                         {
+                            // handler can remove itself, cache the name for metrics
+                            string messageName = m_MessageHandlerNameLookup32[hash];
                             messageHandler32(sender, reader);
-                            m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, m_MessageHandlerNameLookup32[hash], bytesCount);
+                            m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, messageName, bytesCount);
                         }
                         break;
                     case HashSize.VarIntEightBytes:
                         if (m_NamedMessageHandlers64.TryGetValue(hash, out HandleNamedMessageDelegate messageHandler64))
                         {
+                            // handler can remove itself, cache the name for metrics
+                            string messageName = m_MessageHandlerNameLookup64[hash];
                             messageHandler64(sender, reader);
-                            m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, m_MessageHandlerNameLookup64[hash], bytesCount);
+                            m_NetworkManager.NetworkMetrics.TrackNamedMessageReceived(sender, messageName, bytesCount);
                         }
                         break;
                 }
@@ -220,6 +255,20 @@ namespace Unity.Netcode
                     hash = XXHash.Hash64(messageName);
                     break;
             }
+            if (m_NetworkManager.IsHost)
+            {
+                if (clientId == m_NetworkManager.LocalClientId)
+                {
+                    InvokeNamedMessage(
+                        hash,
+                        m_NetworkManager.LocalClientId,
+                        new FastBufferReader(messageStream, Allocator.None),
+                        0
+                    );
+
+                    return;
+                }
+            }
 
             var message = new NamedMessage
             {
@@ -251,7 +300,7 @@ namespace Unity.Netcode
 
             if (clientIds == null)
             {
-                throw new ArgumentNullException("You must pass in a valid clientId List");
+                throw new ArgumentNullException(nameof(clientIds), "You must pass in a valid clientId List");
             }
 
             ulong hash = 0;
@@ -264,6 +313,21 @@ namespace Unity.Netcode
                     hash = XXHash.Hash64(messageName);
                     break;
             }
+            if (m_NetworkManager.IsHost)
+            {
+                for (var i = 0; i < clientIds.Count; ++i)
+                {
+                    if (clientIds[i] == m_NetworkManager.LocalClientId)
+                    {
+                        InvokeNamedMessage(
+                            hash,
+                            m_NetworkManager.LocalClientId,
+                            new FastBufferReader(messageStream, Allocator.None),
+                            0
+                        );
+                    }
+                }
+            }
             var message = new NamedMessage
             {
                 Hash = hash,

Runtime/Messaging/DeferredMessageManager.cs

@@ -1,6 +1,5 @@
 using System.Collections.Generic;
 using Unity.Collections;
-using Time = UnityEngine.Time;
 
 namespace Unity.Netcode
 {
@@ -49,7 +48,7 @@ namespace Unity.Netcode
             {
                 triggerInfo = new TriggerInfo
                 {
-                    Expiry = Time.realtimeSinceStartup + m_NetworkManager.NetworkConfig.SpawnTimeout,
+                    Expiry = m_NetworkManager.RealTimeProvider.RealTimeSinceStartup + m_NetworkManager.NetworkConfig.SpawnTimeout,
                     TriggerData = new NativeList<TriggerData>(Allocator.Persistent)
                 };
                 triggers[key] = triggerInfo;
@@ -77,7 +76,7 @@ namespace Unity.Netcode
                 int index = 0;
                 foreach (var kvp2 in kvp.Value)
                 {
-                    if (kvp2.Value.Expiry < Time.realtimeSinceStartup)
+                    if (kvp2.Value.Expiry < m_NetworkManager.RealTimeProvider.RealTimeSinceStartup)
                     {
                         staleKeys[index++] = kvp2.Key;
                         PurgeTrigger(kvp.Key, kvp2.Key, kvp2.Value);

Runtime/Messaging/DisconnectReasonMessage.cs

@@ -0,0 +1,46 @@
+namespace Unity.Netcode
+{
+    internal struct DisconnectReasonMessage : INetworkMessage
+    {
+        public string Reason;
+
+        public int Version => 0;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
+        {
+            string reasonSent = Reason ?? string.Empty;
+
+            // Since we don't send a ConnectionApprovedMessage, the version for this message is encded with the message
+            // itself. However, note that we HAVE received a ConnectionRequestMessage, so we DO have a valid targetVersion
+            // on this side of things - we just have to make sure the receiving side knows what version we sent it,
+            // since whoever has the higher version number is responsible for versioning and they may be the one
+            // with the higher version number.
+            BytePacker.WriteValueBitPacked(writer, Version);
+
+            if (writer.TryBeginWrite(FastBufferWriter.GetWriteSize(reasonSent)))
+            {
+                writer.WriteValue(reasonSent);
+            }
+            else
+            {
+                writer.WriteValueSafe(string.Empty);
+                NetworkLog.LogWarning(
+                    "Disconnect reason didn't fit. Disconnected without sending a reason. Consider shortening the reason string.");
+            }
+        }
+
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
+        {
+            // Since we don't get a ConnectionApprovedMessage, the version for this message is encded with the message
+            // itself. This will override what we got from MessagingSystem... which will always be 0 here.
+            ByteUnpacker.ReadValueBitPacked(reader, out receivedMessageVersion);
+            reader.ReadValueSafe(out Reason);
+            return true;
+        }
+
+        public void Handle(ref NetworkContext context)
+        {
+            ((NetworkManager)context.SystemOwner).DisconnectReason = Reason;
+        }
+    };
+}

Runtime/Messaging/DisconnectReasonMessage.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d7742516058394f96999464f3ea32c71
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/Messaging/INetworkMessage.cs

@@ -40,8 +40,9 @@ namespace Unity.Netcode
     /// </summary>
     internal interface INetworkMessage
     {
-        void Serialize(FastBufferWriter writer);
+        void Serialize(FastBufferWriter writer, int targetVersion);
-        bool Deserialize(FastBufferReader reader, ref NetworkContext context);
+        bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion);
         void Handle(ref NetworkContext context);
+        int Version { get; }
     }
 }

Runtime/Messaging/Messages/ChangeOwnershipMessage.cs

@@ -2,22 +2,26 @@ namespace Unity.Netcode
 {
     internal struct ChangeOwnershipMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public ulong OwnerClientId;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, OwnerClientId);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
                 return false;
             }
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
             {
                 networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);

Runtime/Messaging/Messages/ConnectionApprovedMessage.cs

@@ -1,10 +1,12 @@
-using System;
 using System.Collections.Generic;
+using Unity.Collections;
 
 namespace Unity.Netcode
 {
     internal struct ConnectionApprovedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong OwnerClientId;
         public int NetworkTick;
 
@@ -13,14 +15,26 @@ namespace Unity.Netcode
 
         private FastBufferReader m_ReceivedSceneObjectData;
 
-        public void Serialize(FastBufferWriter writer)
+        public NativeArray<MessageVersionData> MessageVersions;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            if (!writer.TryBeginWrite(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            BytePacker.WriteValueBitPacked(writer, MessageVersions.Length);
+            foreach (var messageVersion in MessageVersions)
             {
-                throw new OverflowException($"Not enough space in the write buffer to serialize {nameof(ConnectionApprovedMessage)}");
+                messageVersion.Serialize(writer);
             }
-            writer.WriteValue(OwnerClientId);
+            // ============================================================
-            writer.WriteValue(NetworkTick);
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            BytePacker.WriteValueBitPacked(writer, OwnerClientId);
+            BytePacker.WriteValueBitPacked(writer, NetworkTick);
 
             uint sceneObjectCount = 0;
             if (SpawnedObjectsList != null)
@@ -39,17 +53,19 @@ namespace Unity.Netcode
                         ++sceneObjectCount;
                     }
                 }
+
                 writer.Seek(pos);
-                writer.WriteValue(sceneObjectCount);
+                // Can't pack this value because its space is reserved, so it needs to always use all the reserved space.
+                writer.WriteValueSafe(sceneObjectCount);
                 writer.Seek(writer.Length);
             }
             else
             {
-                writer.WriteValue(sceneObjectCount);
+                writer.WriteValueSafe(sceneObjectCount);
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -57,13 +73,36 @@ namespace Unity.Netcode
                 return false;
             }
 
-            if (!reader.TryBeginRead(sizeof(ulong) + sizeof(int) + sizeof(int)))
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            ByteUnpacker.ReadValueBitPacked(reader, out int length);
+            var messageHashesInOrder = new NativeArray<uint>(length, Allocator.Temp);
+            for (var i = 0; i < length; ++i)
             {
-                throw new OverflowException($"Not enough space in the buffer to read {nameof(ConnectionApprovedMessage)}");
+                var messageVersion = new MessageVersionData();
-            }
+                messageVersion.Deserialize(reader);
+                networkManager.MessagingSystem.SetVersion(context.SenderId, messageVersion.Hash, messageVersion.Version);
+                messageHashesInOrder[i] = messageVersion.Hash;
 
-            reader.ReadValue(out OwnerClientId);
+                // Update the received version since this message will always be passed version 0, due to the map not
-            reader.ReadValue(out NetworkTick);
+                // being initialized until just now.
+                var messageType = networkManager.MessagingSystem.GetMessageForHash(messageVersion.Hash);
+                if (messageType == typeof(ConnectionApprovedMessage))
+                {
+                    receivedMessageVersion = messageVersion.Version;
+                }
+            }
+            networkManager.MessagingSystem.SetServerMessageOrder(messageHashesInOrder);
+            messageHashesInOrder.Dispose();
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
+            ByteUnpacker.ReadValueBitPacked(reader, out OwnerClientId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkTick);
             m_ReceivedSceneObjectData = reader;
             return true;
         }
@@ -79,12 +118,13 @@ namespace Unity.Netcode
             networkManager.NetworkTickSystem.Reset(networkManager.NetworkTimeSystem.LocalTime, networkManager.NetworkTimeSystem.ServerTime);
 
             networkManager.LocalClient = new NetworkClient() { ClientId = networkManager.LocalClientId };
+            networkManager.IsApproved = true;
 
             // Only if scene management is disabled do we handle NetworkObject synchronization at this point
             if (!networkManager.NetworkConfig.EnableSceneManagement)
             {
                 networkManager.SpawnManager.DestroySceneObjects();
-                m_ReceivedSceneObjectData.ReadValue(out uint sceneObjectCount);
+                m_ReceivedSceneObjectData.ReadValueSafe(out uint sceneObjectCount);
 
                 // Deserializing NetworkVariable data is deferred from Receive() to Handle to avoid needing
                 // to create a list to hold the data. This is a breach of convention for performance reasons.

Runtime/Messaging/Messages/ConnectionRequestMessage.cs

@@ -1,15 +1,35 @@
+using Unity.Collections;
+
 namespace Unity.Netcode
 {
     internal struct ConnectionRequestMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong ConfigHash;
 
         public byte[] ConnectionData;
 
         public bool ShouldSendConnectionData;
 
-        public void Serialize(FastBufferWriter writer)
+        public NativeArray<MessageVersionData> MessageVersions;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            BytePacker.WriteValueBitPacked(writer, MessageVersions.Length);
+            foreach (var messageVersion in MessageVersions)
+            {
+                messageVersion.Serialize(writer);
+            }
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
             if (ShouldSendConnectionData)
             {
                 writer.WriteValueSafe(ConfigHash);
@@ -21,7 +41,7 @@ namespace Unity.Netcode
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsServer)
@@ -29,6 +49,30 @@ namespace Unity.Netcode
                 return false;
             }
 
+            // ============================================================
+            // BEGIN FORBIDDEN SEGMENT
+            // DO NOT CHANGE THIS HEADER. Everything added to this message
+            // must go AFTER the message version header.
+            // ============================================================
+            ByteUnpacker.ReadValueBitPacked(reader, out int length);
+            for (var i = 0; i < length; ++i)
+            {
+                var messageVersion = new MessageVersionData();
+                messageVersion.Deserialize(reader);
+                networkManager.MessagingSystem.SetVersion(context.SenderId, messageVersion.Hash, messageVersion.Version);
+
+                // Update the received version since this message will always be passed version 0, due to the map not
+                // being initialized until just now.
+                var messageType = networkManager.MessagingSystem.GetMessageForHash(messageVersion.Hash);
+                if (messageType == typeof(ConnectionRequestMessage))
+                {
+                    receivedMessageVersion = messageVersion.Version;
+                }
+            }
+            // ============================================================
+            // END FORBIDDEN SEGMENT
+            // ============================================================
+
             if (networkManager.NetworkConfig.ConnectionApproval)
             {
                 if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(ConfigHash) + FastBufferWriter.GetWriteSize<int>()))

Runtime/Messaging/Messages/CreateObjectMessage.cs

@@ -2,15 +2,17 @@ namespace Unity.Netcode
 {
     internal struct CreateObjectMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public NetworkObject.SceneObject ObjectInfo;
         private FastBufferReader m_ReceivedNetworkVariableData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             ObjectInfo.Serialize(writer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -21,7 +23,7 @@ namespace Unity.Netcode
             ObjectInfo.Deserialize(reader);
             if (!networkManager.NetworkConfig.ForceSamePrefabs && !networkManager.SpawnManager.HasPrefab(ObjectInfo))
             {
-                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnAddPrefab, ObjectInfo.Header.Hash, reader, ref context);
+                networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnAddPrefab, ObjectInfo.Hash, reader, ref context);
                 return false;
             }
             m_ReceivedNetworkVariableData = reader;

Runtime/Messaging/Messages/DestroyObjectMessage.cs

@@ -2,15 +2,18 @@ namespace Unity.Netcode
 {
     internal struct DestroyObjectMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public bool DestroyGameObject;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            writer.WriteValueSafe(DestroyGameObject);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -18,7 +21,8 @@ namespace Unity.Netcode
                 return false;
             }
 
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
+            reader.ReadValueSafe(out DestroyGameObject);
 
             if (!networkManager.SpawnManager.SpawnedObjects.TryGetValue(NetworkObjectId, out var networkObject))
             {

Runtime/Messaging/Messages/MessageMetadata.cs

@@ -0,0 +1,23 @@
+namespace Unity.Netcode
+{
+    /// <summary>
+    /// Conveys a version number on a remote node for the given message (identified by its hash)
+    /// </summary>
+    internal struct MessageVersionData
+    {
+        public uint Hash;
+        public int Version;
+
+        public void Serialize(FastBufferWriter writer)
+        {
+            writer.WriteValueSafe(Hash);
+            BytePacker.WriteValueBitPacked(writer, Version);
+        }
+
+        public void Deserialize(FastBufferReader reader)
+        {
+            reader.ReadValueSafe(out Hash);
+            ByteUnpacker.ReadValueBitPacked(reader, out Version);
+        }
+    }
+}

Runtime/Messaging/Messages/MessageMetadata.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 754d727b316b4263a2fa0d4c54fdad52
+timeCreated: 1666895514

Runtime/Messaging/Messages/NamedMessage.cs

@@ -2,18 +2,20 @@ namespace Unity.Netcode
 {
     internal struct NamedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong Hash;
         public FastBufferWriter SendData;
 
         private FastBufferReader m_ReceiveData;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteValueSafe(Hash);
             writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             reader.ReadValueSafe(out Hash);
             m_ReceiveData = reader;

Runtime/Messaging/Messages/NetworkVariableDeltaMessage.cs

@@ -12,6 +12,8 @@ namespace Unity.Netcode
     /// </summary>
     internal struct NetworkVariableDeltaMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
         public ushort NetworkBehaviourIndex;
 
@@ -21,15 +23,15 @@ namespace Unity.Netcode
 
         private FastBufferReader m_ReceivedNetworkVariableData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
             {
                 throw new OverflowException($"Not enough space in the buffer to write {nameof(NetworkVariableDeltaMessage)}");
             }
 
-            writer.WriteValue(NetworkObjectId);
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
-            writer.WriteValue(NetworkBehaviourIndex);
+            BytePacker.WriteValueBitPacked(writer, NetworkBehaviourIndex);
 
             for (int i = 0; i < NetworkBehaviour.NetworkVariableFields.Count; i++)
             {
@@ -38,7 +40,7 @@ namespace Unity.Netcode
                     // This var does not belong to the currently iterating delivery group.
                     if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                     {
-                        writer.WriteValueSafe((ushort)0);
+                        BytePacker.WriteValueBitPacked(writer, (ushort)0);
                     }
                     else
                     {
@@ -62,11 +64,21 @@ namespace Unity.Netcode
                     shouldWrite = false;
                 }
 
+                // The object containing the behaviour we're about to process is about to be shown to this client
+                // As a result, the client will get the fully serialized NetworkVariable and would be confused by
+                // an extraneous delta
+                if (NetworkBehaviour.NetworkManager.ObjectsToShowToClient.ContainsKey(TargetClientId) &&
+                    NetworkBehaviour.NetworkManager.ObjectsToShowToClient[TargetClientId]
+                    .Contains(NetworkBehaviour.NetworkObject))
+                {
+                    shouldWrite = false;
+                }
+
                 if (NetworkBehaviour.NetworkManager.NetworkConfig.EnsureNetworkVariableLengthSafety)
                 {
                     if (!shouldWrite)
                     {
-                        BytePacker.WriteValueBitPacked(writer, 0);
+                        BytePacker.WriteValueBitPacked(writer, (ushort)0);
                     }
                 }
                 else
@@ -94,12 +106,6 @@ namespace Unity.Netcode
                         networkVariable.WriteDelta(writer);
                     }
 
-                    if (!NetworkBehaviour.NetworkVariableIndexesToResetSet.Contains(i))
-                    {
-                        NetworkBehaviour.NetworkVariableIndexesToResetSet.Add(i);
-                        NetworkBehaviour.NetworkVariableIndexesToReset.Add(i);
-                    }
-
                     NetworkBehaviour.NetworkManager.NetworkMetrics.TrackNetworkVariableDeltaSent(
                         TargetClientId,
                         NetworkBehaviour.NetworkObject,
@@ -110,15 +116,10 @@ namespace Unity.Netcode
             }
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
-            if (!reader.TryBeginRead(FastBufferWriter.GetWriteSize(NetworkObjectId) + FastBufferWriter.GetWriteSize(NetworkBehaviourIndex)))
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
-            {
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkBehaviourIndex);
-                throw new OverflowException($"Not enough data in the buffer to read {nameof(NetworkVariableDeltaMessage)}");
-            }
-
-            reader.ReadValue(out NetworkObjectId);
-            reader.ReadValue(out NetworkBehaviourIndex);
 
             m_ReceivedNetworkVariableData = reader;
 

Runtime/Messaging/Messages/ParentSyncMessage.cs

@@ -1,32 +1,65 @@
+using UnityEngine;
+
 namespace Unity.Netcode
 {
     internal struct ParentSyncMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public ulong NetworkObjectId;
 
-        public bool IsReparented;
+        private byte m_BitField;
+
+        public bool WorldPositionStays
+        {
+            get => ByteUtility.GetBit(m_BitField, 0);
+            set => ByteUtility.SetBit(ref m_BitField, 0, value);
+        }
 
         //If(Metadata.IsReparented)
-        public bool IsLatestParentSet;
+        public bool IsLatestParentSet
+        {
+            get => ByteUtility.GetBit(m_BitField, 1);
+            set => ByteUtility.SetBit(ref m_BitField, 1, value);
+        }
 
         //If(IsLatestParentSet)
         public ulong? LatestParent;
 
-        public void Serialize(FastBufferWriter writer)
+        // Is set when the parent should be removed (similar to IsReparented functionality but only for removing the parent)
+        public bool RemoveParent
         {
-            writer.WriteValueSafe(NetworkObjectId);
+            get => ByteUtility.GetBit(m_BitField, 2);
-            writer.WriteValueSafe(IsReparented);
+            set => ByteUtility.SetBit(ref m_BitField, 2, value);
-            if (IsReparented)
+        }
+
+        // These additional properties are used to synchronize clients with the current position,
+        // rotation, and scale after parenting/de-parenting (world/local space relative). This
+        // allows users to control the final child's transform values without having to have a
+        // NetworkTransform component on the child. (i.e. picking something up)
+        public Vector3 Position;
+        public Quaternion Rotation;
+        public Vector3 Scale;
+
+        public void Serialize(FastBufferWriter writer, int targetVersion)
+        {
+            BytePacker.WriteValueBitPacked(writer, NetworkObjectId);
+            writer.WriteValueSafe(m_BitField);
+            if (!RemoveParent)
             {
-                writer.WriteValueSafe(IsLatestParentSet);
                 if (IsLatestParentSet)
                 {
-                    writer.WriteValueSafe((ulong)LatestParent);
+                    BytePacker.WriteValueBitPacked(writer, LatestParent.Value);
-                }
                 }
             }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+            // Whether parenting or removing a parent, we always update the position, rotation, and scale
+            writer.WriteValueSafe(Position);
+            writer.WriteValueSafe(Rotation);
+            writer.WriteValueSafe(Scale);
+        }
+
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
@@ -34,24 +67,27 @@ namespace Unity.Netcode
                 return false;
             }
 
-            reader.ReadValueSafe(out NetworkObjectId);
+            ByteUnpacker.ReadValueBitPacked(reader, out NetworkObjectId);
-            reader.ReadValueSafe(out IsReparented);
+            reader.ReadValueSafe(out m_BitField);
-            if (IsReparented)
+            if (!RemoveParent)
             {
-                reader.ReadValueSafe(out IsLatestParentSet);
                 if (IsLatestParentSet)
                 {
-                    reader.ReadValueSafe(out ulong latestParent);
+                    ByteUnpacker.ReadValueBitPacked(reader, out ulong latestParent);
                     LatestParent = latestParent;
                 }
             }
 
+            // Whether parenting or removing a parent, we always update the position, rotation, and scale
+            reader.ReadValueSafe(out Position);
+            reader.ReadValueSafe(out Rotation);
+            reader.ReadValueSafe(out Scale);
+
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(NetworkObjectId))
             {
                 networkManager.DeferredMessageManager.DeferMessage(IDeferredMessageManager.TriggerType.OnSpawn, NetworkObjectId, reader, ref context);
                 return false;
             }
-
             return true;
         }
 
@@ -59,8 +95,22 @@ namespace Unity.Netcode
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             var networkObject = networkManager.SpawnManager.SpawnedObjects[NetworkObjectId];
-            networkObject.SetNetworkParenting(IsReparented, LatestParent);
+            networkObject.SetNetworkParenting(LatestParent, WorldPositionStays);
-            networkObject.ApplyNetworkParenting();
+            networkObject.ApplyNetworkParenting(RemoveParent);
+
+            // We set all of the transform values after parenting as they are
+            // the values of the server-side post-parenting transform values
+            if (!WorldPositionStays)
+            {
+                networkObject.transform.localPosition = Position;
+                networkObject.transform.localRotation = Rotation;
+            }
+            else
+            {
+                networkObject.transform.position = Position;
+                networkObject.transform.rotation = Rotation;
+            }
+            networkObject.transform.localScale = Scale;
         }
     }
 }

Runtime/Messaging/Messages/RpcMessages.cs

@@ -1,6 +1,6 @@
 using System;
-using UnityEngine;
 using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -8,24 +8,17 @@ namespace Unity.Netcode
     {
         public static unsafe void Serialize(ref FastBufferWriter writer, ref RpcMetadata metadata, ref FastBufferWriter payload)
         {
-            if (!writer.TryBeginWrite(FastBufferWriter.GetWriteSize<RpcMetadata>() + payload.Length))
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkObjectId);
-            {
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkBehaviourId);
-                throw new OverflowException("Not enough space in the buffer to store RPC data.");
+            BytePacker.WriteValueBitPacked(writer, metadata.NetworkRpcMethodId);
-            }
+            writer.WriteBytesSafe(payload.GetUnsafePtr(), payload.Length);
-
-            writer.WriteValue(metadata);
-            writer.WriteBytes(payload.GetUnsafePtr(), payload.Length);
         }
 
         public static unsafe bool Deserialize(ref FastBufferReader reader, ref NetworkContext context, ref RpcMetadata metadata, ref FastBufferReader payload)
         {
-            int metadataSize = FastBufferWriter.GetWriteSize<RpcMetadata>();
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkObjectId);
-            if (!reader.TryBeginRead(metadataSize))
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkBehaviourId);
-            {
+            ByteUnpacker.ReadValueBitPacked(reader, out metadata.NetworkRpcMethodId);
-                throw new InvalidOperationException("Not enough data in the buffer to read RPC meta.");
-            }
-
-            reader.ReadValue(out metadata);
 
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(metadata.NetworkObjectId))
@@ -46,7 +39,7 @@ namespace Unity.Netcode
                 return false;
             }
 
-            payload = new FastBufferReader(reader.GetUnsafePtr() + metadataSize, Allocator.None, reader.Length - metadataSize);
+            payload = new FastBufferReader(reader.GetUnsafePtrAtCurrentPosition(), Allocator.None, reader.Length - reader.Position);
 
 #if DEVELOPMENT_BUILD || UNITY_EDITOR
             if (NetworkManager.__rpc_name_table.TryGetValue(metadata.NetworkRpcMethodId, out var rpcMethodName))
@@ -92,17 +85,19 @@ namespace Unity.Netcode
 
     internal struct ServerRpcMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public RpcMetadata Metadata;
 
         public FastBufferWriter WriteBuffer;
         public FastBufferReader ReadBuffer;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
         }
 
-        public unsafe bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public unsafe bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
         }
@@ -125,17 +120,19 @@ namespace Unity.Netcode
 
     internal struct ClientRpcMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public RpcMetadata Metadata;
 
         public FastBufferWriter WriteBuffer;
         public FastBufferReader ReadBuffer;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             RpcMessageHelpers.Serialize(ref writer, ref Metadata, ref WriteBuffer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             return RpcMessageHelpers.Deserialize(ref reader, ref context, ref Metadata, ref ReadBuffer);
         }

Runtime/Messaging/Messages/SceneEventMessage.cs

@@ -4,16 +4,18 @@ namespace Unity.Netcode
     // like most of the other messages when we have some more time and can come back and refactor this.
     internal struct SceneEventMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public SceneEventData EventData;
 
         private FastBufferReader m_ReceivedData;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             EventData.Serialize(writer);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             m_ReceivedData = reader;
             return true;

Runtime/Messaging/Messages/ServerLogMessage.cs

@@ -2,6 +2,8 @@ namespace Unity.Netcode
 {
     internal struct ServerLogMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public NetworkLog.LogType LogType;
         // It'd be lovely to be able to replace this with FixedString or NativeArray...
         // But it's not really practical. On the sending side, the user is likely to want
@@ -11,13 +13,13 @@ namespace Unity.Netcode
         public string Message;
 
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteValueSafe(LogType);
             BytePacker.WriteValuePacked(writer, Message);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (networkManager.IsServer && networkManager.NetworkConfig.EnableNetworkLogs)

Runtime/Messaging/Messages/TimeSyncMessage.cs

@@ -2,21 +2,23 @@ namespace Unity.Netcode
 {
     internal struct TimeSyncMessage : INetworkMessage, INetworkSerializeByMemcpy
     {
+        public int Version => 0;
+
         public int Tick;
 
-        public void Serialize(FastBufferWriter writer)
+        public void Serialize(FastBufferWriter writer, int targetVersion)
         {
-            writer.WriteValueSafe(this);
+            BytePacker.WriteValueBitPacked(writer, Tick);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             var networkManager = (NetworkManager)context.SystemOwner;
             if (!networkManager.IsClient)
             {
                 return false;
             }
-            reader.ReadValueSafe(out this);
+            ByteUnpacker.ReadValueBitPacked(reader, out Tick);
             return true;
         }
 

Runtime/Messaging/Messages/UnnamedMessage.cs

@@ -2,15 +2,17 @@ namespace Unity.Netcode
 {
     internal struct UnnamedMessage : INetworkMessage
     {
+        public int Version => 0;
+
         public FastBufferWriter SendData;
         private FastBufferReader m_ReceivedData;
 
-        public unsafe void Serialize(FastBufferWriter writer)
+        public unsafe void Serialize(FastBufferWriter writer, int targetVersion)
         {
             writer.WriteBytesSafe(SendData.GetUnsafePtr(), SendData.Length);
         }
 
-        public bool Deserialize(FastBufferReader reader, ref NetworkContext context)
+        public bool Deserialize(FastBufferReader reader, ref NetworkContext context, int receivedMessageVersion)
         {
             m_ReceivedData = reader;
             return true;

Runtime/Messaging/MessagingSystem.cs

@@ -2,12 +2,18 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
+using System.Text;
 using Unity.Collections;
 using Unity.Collections.LowLevel.Unsafe;
 using UnityEngine;
 
 namespace Unity.Netcode
 {
+    internal class HandlerNotRegisteredException : SystemException
+    {
+        public HandlerNotRegisteredException() { }
+        public HandlerNotRegisteredException(string issue) : base(issue) { }
+    }
 
     internal class InvalidMessageStructureException : SystemException
     {
@@ -36,20 +42,27 @@ namespace Unity.Netcode
             {
                 Writer = new FastBufferWriter(writerSize, writerAllocator, maxWriterSize);
                 NetworkDelivery = delivery;
-                BatchHeader = default;
+                BatchHeader = new BatchHeader { Magic = BatchHeader.MagicValue };
             }
         }
 
         internal delegate void MessageHandler(FastBufferReader reader, ref NetworkContext context, MessagingSystem system);
+        internal delegate int VersionGetter();
 
         private NativeList<ReceiveQueueItem> m_IncomingMessageQueue = new NativeList<ReceiveQueueItem>(16, Allocator.Persistent);
 
-        private MessageHandler[] m_MessageHandlers = new MessageHandler[255];
+        // These array will grow as we need more message handlers. 4 is just a starting size.
-        private Type[] m_ReverseTypeMap = new Type[255];
+        private MessageHandler[] m_MessageHandlers = new MessageHandler[4];
+        private Type[] m_ReverseTypeMap = new Type[4];
 
         private Dictionary<Type, uint> m_MessageTypes = new Dictionary<Type, uint>();
         private Dictionary<ulong, NativeList<SendQueueItem>> m_SendQueues = new Dictionary<ulong, NativeList<SendQueueItem>>();
 
+        // This is m_PerClientMessageVersion[clientId][messageType] = version
+        private Dictionary<ulong, Dictionary<Type, int>> m_PerClientMessageVersions = new Dictionary<ulong, Dictionary<Type, int>>();
+        private Dictionary<uint, Type> m_MessagesByHash = new Dictionary<uint, Type>();
+        private Dictionary<Type, int> m_LocalVersions = new Dictionary<Type, int>();
+
         private List<INetworkHooks> m_Hooks = new List<INetworkHooks>();
 
         private uint m_HighMessageType;
@@ -59,6 +72,7 @@ namespace Unity.Netcode
 
         internal Type[] MessageTypes => m_ReverseTypeMap;
         internal MessageHandler[] MessageHandlers => m_MessageHandlers;
+
         internal uint MessageHandlerCount => m_HighMessageType;
 
         internal uint GetMessageType(Type t)
@@ -67,12 +81,40 @@ namespace Unity.Netcode
         }
 
         public const int NON_FRAGMENTED_MESSAGE_MAX_SIZE = 1300;
-        public const int FRAGMENTED_MESSAGE_MAX_SIZE = BytePacker.BitPackedIntMax;
+        public const int FRAGMENTED_MESSAGE_MAX_SIZE = int.MaxValue;
 
         internal struct MessageWithHandler
         {
             public Type MessageType;
             public MessageHandler Handler;
+            public VersionGetter GetVersion;
+        }
+
+        internal List<MessageWithHandler> PrioritizeMessageOrder(List<MessageWithHandler> allowedTypes)
+        {
+            var prioritizedTypes = new List<MessageWithHandler>();
+
+            // first pass puts the priority message in the first indices
+            // Those are the messages that must be delivered in order to allow re-ordering the others later
+            foreach (var t in allowedTypes)
+            {
+                if (t.MessageType.FullName == typeof(ConnectionRequestMessage).FullName ||
+                    t.MessageType.FullName == typeof(ConnectionApprovedMessage).FullName)
+                {
+                    prioritizedTypes.Add(t);
+                }
+            }
+
+            foreach (var t in allowedTypes)
+            {
+                if (t.MessageType.FullName != typeof(ConnectionRequestMessage).FullName &&
+                    t.MessageType.FullName != typeof(ConnectionApprovedMessage).FullName)
+                {
+                    prioritizedTypes.Add(t);
+                }
+            }
+
+            return prioritizedTypes;
         }
 
         public MessagingSystem(IMessageSender messageSender, object owner, IMessageProvider provider = null)
@@ -89,6 +131,7 @@ namespace Unity.Netcode
                 var allowedTypes = provider.GetMessages();
 
                 allowedTypes.Sort((a, b) => string.CompareOrdinal(a.MessageType.FullName, b.MessageType.FullName));
+                allowedTypes = PrioritizeMessageOrder(allowedTypes);
                 foreach (var type in allowedTypes)
                 {
                     RegisterMessageType(type);
@@ -143,9 +186,34 @@ namespace Unity.Netcode
 
         private void RegisterMessageType(MessageWithHandler messageWithHandler)
         {
+            // if we are out of space, perform amortized linear growth
+            if (m_HighMessageType == m_MessageHandlers.Length)
+            {
+                Array.Resize(ref m_MessageHandlers, 2 * m_MessageHandlers.Length);
+                Array.Resize(ref m_ReverseTypeMap, 2 * m_ReverseTypeMap.Length);
+            }
+
             m_MessageHandlers[m_HighMessageType] = messageWithHandler.Handler;
             m_ReverseTypeMap[m_HighMessageType] = messageWithHandler.MessageType;
+            m_MessagesByHash[XXHash.Hash32(messageWithHandler.MessageType.FullName)] = messageWithHandler.MessageType;
             m_MessageTypes[messageWithHandler.MessageType] = m_HighMessageType++;
+            m_LocalVersions[messageWithHandler.MessageType] = messageWithHandler.GetVersion();
+        }
+
+        public int GetLocalVersion(Type messageType)
+        {
+            return m_LocalVersions[messageType];
+        }
+
+        internal static string ByteArrayToString(byte[] ba, int offset, int count)
+        {
+            var hex = new StringBuilder(ba.Length * 2);
+            for (int i = offset; i < offset + count; ++i)
+            {
+                hex.AppendFormat("{0:x2} ", ba[i]);
+            }
+
+            return hex.ToString();
         }
 
         internal void HandleIncomingData(ulong clientId, ArraySegment<byte> data, float receiveTime)
@@ -158,18 +226,38 @@ namespace Unity.Netcode
                         new FastBufferReader(nativeData + data.Offset, Allocator.None, data.Count);
                     if (!batchReader.TryBeginRead(sizeof(BatchHeader)))
                     {
-                        NetworkLog.LogWarning("Received a packet too small to contain a BatchHeader. Ignoring it.");
+                        NetworkLog.LogError("Received a packet too small to contain a BatchHeader. Ignoring it.");
                         return;
                     }
 
                     batchReader.ReadValue(out BatchHeader batchHeader);
 
-                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    if (batchHeader.Magic != BatchHeader.MagicValue)
                     {
-                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        NetworkLog.LogError($"Received a packet with an invalid Magic Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
                     }
 
-                    for (var messageIdx = 0; messageIdx < batchHeader.BatchSize; ++messageIdx)
+                    if (batchHeader.BatchSize != data.Count)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Batch Size Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Expected Size: {batchHeader.BatchSize}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    var hash = XXHash.Hash64(batchReader.GetUnsafePtrAtCurrentPosition(), batchReader.Length - batchReader.Position);
+
+                    if (hash != batchHeader.BatchHash)
+                    {
+                        NetworkLog.LogError($"Received a packet with an invalid Hash Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Received Hash: {batchHeader.BatchHash}, Calculated Hash: {hash}, Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
+                        return;
+                    }
+
+                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
+                    {
+                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
+                    }
+
+                    for (var messageIdx = 0; messageIdx < batchHeader.BatchCount; ++messageIdx)
                     {
 
                         var messageHeader = new MessageHeader();
@@ -181,7 +269,7 @@ namespace Unity.Netcode
                         }
                         catch (OverflowException)
                         {
-                            NetworkLog.LogWarning("Received a batch that didn't have enough data for all of its batches, ending early!");
+                            NetworkLog.LogError("Received a batch that didn't have enough data for all of its batches, ending early!");
                             throw;
                         }
 
@@ -189,7 +277,7 @@ namespace Unity.Netcode
 
                         if (!batchReader.TryBeginRead((int)messageHeader.MessageSize))
                         {
-                            NetworkLog.LogWarning("Received a message that claimed a size larger than the packet, ending early!");
+                            NetworkLog.LogError("Received a message that claimed a size larger than the packet, ending early!");
                             return;
                         }
                         m_IncomingMessageQueue.Add(new ReceiveQueueItem
@@ -207,7 +295,7 @@ namespace Unity.Netcode
                     }
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchSize, batchReader.Length);
+                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
                     }
                 }
             }
@@ -226,12 +314,62 @@ namespace Unity.Netcode
             return true;
         }
 
+        internal Type GetMessageForHash(uint messageHash)
+        {
+            if (!m_MessagesByHash.ContainsKey(messageHash))
+            {
+                return null;
+            }
+            return m_MessagesByHash[messageHash];
+        }
+
+        internal void SetVersion(ulong clientId, uint messageHash, int version)
+        {
+            if (!m_MessagesByHash.ContainsKey(messageHash))
+            {
+                return;
+            }
+            var messageType = m_MessagesByHash[messageHash];
+
+            if (!m_PerClientMessageVersions.ContainsKey(clientId))
+            {
+                m_PerClientMessageVersions[clientId] = new Dictionary<Type, int>();
+            }
+
+            m_PerClientMessageVersions[clientId][messageType] = version;
+        }
+
+        internal void SetServerMessageOrder(NativeArray<uint> messagesInIdOrder)
+        {
+            var oldHandlers = m_MessageHandlers;
+            var oldTypes = m_MessageTypes;
+            m_ReverseTypeMap = new Type[messagesInIdOrder.Length];
+            m_MessageHandlers = new MessageHandler[messagesInIdOrder.Length];
+            m_MessageTypes = new Dictionary<Type, uint>();
+
+            for (var i = 0; i < messagesInIdOrder.Length; ++i)
+            {
+                if (!m_MessagesByHash.ContainsKey(messagesInIdOrder[i]))
+                {
+                    continue;
+                }
+                var messageType = m_MessagesByHash[messagesInIdOrder[i]];
+                var oldId = oldTypes[messageType];
+                var handler = oldHandlers[oldId];
+                var newId = (uint)i;
+                m_MessageTypes[messageType] = newId;
+                m_MessageHandlers[newId] = handler;
+                m_ReverseTypeMap[newId] = messageType;
+            }
+        }
+
         public void HandleMessage(in MessageHeader header, FastBufferReader reader, ulong senderId, float timestamp, int serializedHeaderSize)
+        {
+            using (reader)
             {
                 if (header.MessageType >= m_HighMessageType)
                 {
                     Debug.LogWarning($"Received a message with invalid message type value {header.MessageType}");
-                reader.Dispose();
                     return;
                 }
                 var context = new NetworkContext
@@ -247,17 +385,24 @@ namespace Unity.Netcode
                 var type = m_ReverseTypeMap[header.MessageType];
                 if (!CanReceive(senderId, type, reader, ref context))
                 {
-                reader.Dispose();
                     return;
                 }
 
+                var handler = m_MessageHandlers[header.MessageType];
                 for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                 {
                     m_Hooks[hookIdx].OnBeforeReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<MessageHeader>());
                 }
 
-            var handler = m_MessageHandlers[header.MessageType];
+                // This will also log an exception is if the server knows about a message type the client doesn't know
-            using (reader)
+                // about. In this case the handler will be null. It is still an issue the user must deal with: If the
+                // two connecting builds know about different messages, the server should not send a message to a client
+                // that doesn't know about it
+                if (handler == null)
+                {
+                    Debug.LogException(new HandlerNotRegisteredException(header.MessageType.ToString()));
+                }
+                else
                 {
                     // No user-land message handler exceptions should escape the receive loop.
                     // If an exception is throw, the message is ignored.
@@ -278,6 +423,7 @@ namespace Unity.Netcode
                     m_Hooks[hookIdx].OnAfterReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<MessageHeader>());
                 }
             }
+        }
 
         internal unsafe void ProcessIncomingMessageQueue()
         {
@@ -314,7 +460,7 @@ namespace Unity.Netcode
             m_SendQueues.Remove(clientId);
         }
 
-        private unsafe void CleanupDisconnectedClient(ulong clientId)
+        private void CleanupDisconnectedClient(ulong clientId)
         {
             var queue = m_SendQueues[clientId];
             for (var i = 0; i < queue.Length; ++i)
@@ -325,10 +471,67 @@ namespace Unity.Netcode
             queue.Dispose();
         }
 
+        internal void CleanupDisconnectedClients()
+        {
+            var removeList = new NativeList<ulong>(Allocator.Temp);
+            foreach (var clientId in m_PerClientMessageVersions.Keys)
+            {
+                if (!m_SendQueues.ContainsKey(clientId))
+                {
+                    removeList.Add(clientId);
+                }
+            }
+
+            foreach (var clientId in removeList)
+            {
+                m_PerClientMessageVersions.Remove(clientId);
+            }
+        }
+
+        public static int CreateMessageAndGetVersion<T>() where T : INetworkMessage, new()
+        {
+            return new T().Version;
+        }
+
+        internal int GetMessageVersion(Type type, ulong clientId, bool forReceive = false)
+        {
+            if (!m_PerClientMessageVersions.TryGetValue(clientId, out var versionMap))
+            {
+                if (forReceive)
+                {
+                    Debug.LogWarning($"Trying to receive {type.Name} from client {clientId} which is not in a connected state.");
+
+                }
+                else
+                {
+                    Debug.LogWarning($"Trying to send {type.Name} to client {clientId} which is not in a connected state.");
+                }
+                return -1;
+            }
+            if (!versionMap.TryGetValue(type, out var messageVersion))
+            {
+                return -1;
+            }
+
+            return messageVersion;
+        }
+
         public static void ReceiveMessage<T>(FastBufferReader reader, ref NetworkContext context, MessagingSystem system) where T : INetworkMessage, new()
         {
             var message = new T();
-            if (message.Deserialize(reader, ref context))
+            var messageVersion = 0;
+            // Special cases because these are the messages that carry the version info - thus the version info isn't
+            // populated yet when we get these. The first part of these messages always has to be the version data
+            // and can't change.
+            if (typeof(T) != typeof(ConnectionRequestMessage) && typeof(T) != typeof(ConnectionApprovedMessage) && typeof(T) != typeof(DisconnectReasonMessage))
+            {
+                messageVersion = system.GetMessageVersion(typeof(T), context.SenderId, true);
+                if (messageVersion < 0)
+                {
+                    return;
+                }
+            }
+            if (message.Deserialize(reader, ref context, messageVersion))
             {
                 for (var hookIdx = 0; hookIdx < system.m_Hooks.Count; ++hookIdx)
                 {
@@ -366,16 +569,47 @@ namespace Unity.Netcode
                 return 0;
             }
 
+            var largestSerializedSize = 0;
+            var sentMessageVersions = new NativeHashSet<int>(clientIds.Count, Allocator.Temp);
+            for (var i = 0; i < clientIds.Count; ++i)
+            {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+                }
+
+                if (sentMessageVersions.Contains(messageVersion))
+                {
+                    continue;
+                }
+
+                sentMessageVersions.Add(messageVersion);
+
                 var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FRAGMENTED_MESSAGE_MAX_SIZE : NON_FRAGMENTED_MESSAGE_MAX_SIZE;
 
                 using var tmpSerializer = new FastBufferWriter(NON_FRAGMENTED_MESSAGE_MAX_SIZE - FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp, maxSize - FastBufferWriter.GetWriteSize<MessageHeader>());
 
-            message.Serialize(tmpSerializer);
+                message.Serialize(tmpSerializer, messageVersion);
 
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds);
+                var size = SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds, messageVersion);
+                largestSerializedSize = size > largestSerializedSize ? size : largestSerializedSize;
             }
 
-        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds)
+            sentMessageVersions.Dispose();
+
+            return largestSerializedSize;
+        }
+
+        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds, int messageVersionFilter)
             where TMessageType : INetworkMessage
         {
             using var headerSerializer = new FastBufferWriter(FastBufferWriter.GetWriteSize<MessageHeader>(), Allocator.Temp);
@@ -390,6 +624,25 @@ namespace Unity.Netcode
 
             for (var i = 0; i < clientIds.Count; ++i)
             {
+                var messageVersion = 0;
+                // Special case because this is the message that carries the version info - thus the version info isn't
+                // populated yet when we get this. The first part of this message always has to be the version data
+                // and can't change.
+                if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+                {
+                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
+                    if (messageVersion < 0)
+                    {
+                        // Client doesn't know this message exists, don't send it at all.
+                        continue;
+                    }
+
+                    if (messageVersion != messageVersionFilter)
+                    {
+                        continue;
+                    }
+                }
+
                 var clientId = clientIds[i];
 
                 if (!CanSend(clientId, typeof(TMessageType), delivery))
@@ -427,7 +680,7 @@ namespace Unity.Netcode
 
                 writeQueueItem.Writer.WriteBytes(headerSerializer.GetUnsafePtr(), headerSerializer.Length);
                 writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
-                writeQueueItem.BatchHeader.BatchSize++;
+                writeQueueItem.BatchHeader.BatchCount++;
                 for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                 {
                     m_Hooks[hookIdx].OnAfterSendMessage(clientId, ref message, delivery, tmpSerializer.Length + headerSerializer.Length);
@@ -440,8 +693,22 @@ namespace Unity.Netcode
         internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, ulong clientId)
             where TMessageType : INetworkMessage
         {
+            var messageVersion = 0;
+            // Special case because this is the message that carries the version info - thus the version info isn't
+            // populated yet when we get this. The first part of this message always has to be the version data
+            // and can't change.
+            if (typeof(TMessageType) != typeof(ConnectionRequestMessage))
+            {
+                messageVersion = GetMessageVersion(typeof(TMessageType), clientId);
+                if (messageVersion < 0)
+                {
+                    // Client doesn't know this message exists, don't send it at all.
+                    return 0;
+                }
+            }
+
             ulong* clientIds = stackalloc ulong[] { clientId };
-            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
+            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1), messageVersion);
         }
 
         private struct PointerListWrapper<T> : IReadOnlyList<T>
@@ -508,7 +775,7 @@ namespace Unity.Netcode
                 for (var i = 0; i < sendQueueItem.Length; ++i)
                 {
                     ref var queueItem = ref sendQueueItem.ElementAt(i);
-                    if (queueItem.BatchHeader.BatchSize == 0)
+                    if (queueItem.BatchHeader.BatchCount == 0)
                     {
                         queueItem.Writer.Dispose();
                         continue;
@@ -516,23 +783,28 @@ namespace Unity.Netcode
 
                     for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                     {
-                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                     }
 
                     queueItem.Writer.Seek(0);
 #if UNITY_EDITOR || DEVELOPMENT_BUILD
                     // Skipping the Verify and sneaking the write mark in because we know it's fine.
-                    queueItem.Writer.Handle->AllowedWriteMark = 2;
+                    queueItem.Writer.Handle->AllowedWriteMark = sizeof(BatchHeader);
 #endif
+                    queueItem.BatchHeader.BatchHash = XXHash.Hash64(queueItem.Writer.GetUnsafePtr() + sizeof(BatchHeader), queueItem.Writer.Length - sizeof(BatchHeader));
+
+                    queueItem.BatchHeader.BatchSize = queueItem.Writer.Length;
+
                     queueItem.Writer.WriteValue(queueItem.BatchHeader);
 
+
                     try
                     {
                         m_MessageSender.Send(clientId, queueItem.NetworkDelivery, queueItem.Writer);
 
                         for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                         {
-                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchSize, queueItem.Writer.Length, queueItem.NetworkDelivery);
+                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                         }
                     }
                     finally

Runtime/Metrics/NetworkMetrics.cs

@@ -5,17 +5,14 @@ using Unity.Multiplayer.Tools;
 using Unity.Multiplayer.Tools.MetricTypes;
 using Unity.Multiplayer.Tools.NetStats;
 using Unity.Profiling;
-using UnityEngine;
 
 namespace Unity.Netcode
 {
     internal class NetworkMetrics : INetworkMetrics
     {
-        const ulong k_MaxMetricsPerFrame = 1000L;
+        private const ulong k_MaxMetricsPerFrame = 1000L;
-
+        private static Dictionary<uint, string> s_SceneEventTypeNames;
-        static Dictionary<uint, string> s_SceneEventTypeNames;
+        private static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
-
-        static ProfilerMarker s_FrameDispatch = new ProfilerMarker($"{nameof(NetworkMetrics)}.DispatchFrame");
 
         static NetworkMetrics()
         {

Runtime/Metrics/NetworkObjectProvider.cs

@@ -4,7 +4,7 @@ using UnityEngine;
 
 namespace Unity.Netcode
 {
-    class NetworkObjectProvider : INetworkObjectProvider
+    internal class NetworkObjectProvider : INetworkObjectProvider
     {
         private readonly NetworkManager m_NetworkManager;
 

Runtime/NetworkVariable/Collections/NetworkList.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using Unity.Collections;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -11,7 +12,6 @@ namespace Unity.Netcode
     public class NetworkList<T> : NetworkVariableBase where T : unmanaged, IEquatable<T>
     {
         private NativeList<T> m_List = new NativeList<T>(64, Allocator.Persistent);
-        private NativeList<T> m_ListAtLastReset = new NativeList<T>(64, Allocator.Persistent);
         private NativeList<NetworkListEvent<T>> m_DirtyEvents = new NativeList<NetworkListEvent<T>>(64, Allocator.Persistent);
 
         /// <summary>
@@ -38,12 +38,16 @@ namespace Unity.Netcode
             NetworkVariableReadPermission readPerm = DefaultReadPerm,
             NetworkVariableWritePermission writePerm = DefaultWritePerm)
             : base(readPerm, writePerm)
+        {
+            // allow null IEnumerable<T> to mean "no values"
+            if (values != null)
             {
                 foreach (var value in values)
                 {
                     m_List.Add(value);
                 }
             }
+        }
 
         /// <inheritdoc />
         public override void ResetDirty()
@@ -52,7 +56,6 @@ namespace Unity.Netcode
             if (m_DirtyEvents.Length > 0)
             {
                 m_DirtyEvents.Clear();
-                m_ListAtLastReset.CopyFrom(m_List);
             }
         }
 
@@ -63,6 +66,18 @@ namespace Unity.Netcode
             return base.IsDirty() || m_DirtyEvents.Length > 0;
         }
 
+        internal void MarkNetworkObjectDirty()
+        {
+            if (m_NetworkBehaviour == null)
+            {
+                Debug.LogWarning($"NetworkList is written to, but doesn't know its NetworkBehaviour yet. " +
+                                 "Are you modifying a NetworkList before the NetworkObject is spawned?");
+                return;
+            }
+
+            m_NetworkBehaviour.NetworkManager.MarkNetworkObjectDirty(m_NetworkBehaviour.NetworkObject);
+        }
+
         /// <inheritdoc />
         public override void WriteDelta(FastBufferWriter writer)
         {
@@ -122,10 +137,10 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void WriteField(FastBufferWriter writer)
         {
-            writer.WriteValueSafe((ushort)m_ListAtLastReset.Length);
+            writer.WriteValueSafe((ushort)m_List.Length);
-            for (int i = 0; i < m_ListAtLastReset.Length; i++)
+            for (int i = 0; i < m_List.Length; i++)
             {
-                NetworkVariableSerialization<T>.Write(writer, ref m_ListAtLastReset.ElementAt(i));
+                NetworkVariableSerialization<T>.Write(writer, ref m_List.ElementAt(i));
             }
         }
 
@@ -136,7 +151,8 @@ namespace Unity.Netcode
             reader.ReadValueSafe(out ushort count);
             for (int i = 0; i < count; i++)
             {
-                NetworkVariableSerialization<T>.Read(reader, out T value);
+                var value = new T();
+                NetworkVariableSerialization<T>.Read(reader, ref value);
                 m_List.Add(value);
             }
         }
@@ -152,7 +168,8 @@ namespace Unity.Netcode
                 {
                     case NetworkListEvent<T>.EventType.Add:
                         {
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             m_List.Add(value);
 
                             if (OnListChanged != null)
@@ -173,15 +190,25 @@ namespace Unity.Netcode
                                     Index = m_List.Length - 1,
                                     Value = m_List[m_List.Length - 1]
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Insert:
                         {
                             reader.ReadValueSafe(out int index);
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
+
+                            if (index < m_List.Length)
+                            {
                                 m_List.InsertRangeWithBeginEnd(index, index + 1);
                                 m_List[index] = value;
+                            }
+                            else
+                            {
+                                m_List.Add(value);
+                            }
 
                             if (OnListChanged != null)
                             {
@@ -201,12 +228,14 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = m_List[index]
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Remove:
                         {
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             int index = m_List.IndexOf(value);
                             if (index == -1)
                             {
@@ -233,6 +262,7 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -260,13 +290,15 @@ namespace Unity.Netcode
                                     Index = index,
                                     Value = value
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
                     case NetworkListEvent<T>.EventType.Value:
                         {
                             reader.ReadValueSafe(out int index);
-                            NetworkVariableSerialization<T>.Read(reader, out T value);
+                            var value = new T();
+                            NetworkVariableSerialization<T>.Read(reader, ref value);
                             if (index >= m_List.Length)
                             {
                                 throw new Exception("Shouldn't be here, index is higher than list length");
@@ -295,6 +327,7 @@ namespace Unity.Netcode
                                     Value = value,
                                     PreviousValue = previousValue
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -317,6 +350,7 @@ namespace Unity.Netcode
                                 {
                                     Type = eventType
                                 });
+                                MarkNetworkObjectDirty();
                             }
                         }
                         break;
@@ -339,6 +373,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void Add(T item)
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.Add(item);
 
             var listEvent = new NetworkListEvent<T>()
@@ -354,6 +394,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void Clear()
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.Clear();
 
             var listEvent = new NetworkListEvent<T>()
@@ -367,14 +413,20 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public bool Contains(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            int index = m_List.IndexOf(item);
             return index != -1;
         }
 
         /// <inheritdoc />
         public bool Remove(T item)
         {
-            int index = NativeArrayExtensions.IndexOf(m_List, item);
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
+            int index = m_List.IndexOf(item);
             if (index == -1)
             {
                 return false;
@@ -402,9 +454,22 @@ namespace Unity.Netcode
 
         /// <inheritdoc />
         public void Insert(int index, T item)
+        {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
+            if (index < m_List.Length)
             {
                 m_List.InsertRangeWithBeginEnd(index, index + 1);
                 m_List[index] = item;
+            }
+            else
+            {
+                m_List.Add(item);
+            }
 
             var listEvent = new NetworkListEvent<T>()
             {
@@ -419,6 +484,12 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public void RemoveAt(int index)
         {
+            // check write permissions
+            if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+            {
+                throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+            }
+
             m_List.RemoveAt(index);
 
             var listEvent = new NetworkListEvent<T>()
@@ -436,13 +507,21 @@ namespace Unity.Netcode
             get => m_List[index];
             set
             {
+                // check write permissions
+                if (!CanClientWrite(m_NetworkBehaviour.NetworkManager.LocalClientId))
+                {
+                    throw new InvalidOperationException("Client is not allowed to write to this NetworkList");
+                }
+
+                var previousValue = m_List[index];
                 m_List[index] = value;
 
                 var listEvent = new NetworkListEvent<T>()
                 {
                     Type = NetworkListEvent<T>.EventType.Value,
                     Index = index,
-                    Value = value
+                    Value = value,
+                    PreviousValue = previousValue
                 };
 
                 HandleAddListEvent(listEvent);
@@ -452,6 +531,7 @@ namespace Unity.Netcode
         private void HandleAddListEvent(NetworkListEvent<T> listEvent)
         {
             m_DirtyEvents.Add(listEvent);
+            MarkNetworkObjectDirty();
             OnListChanged?.Invoke(listEvent);
         }
 
@@ -475,7 +555,6 @@ namespace Unity.Netcode
         public override void Dispose()
         {
             m_List.Dispose();
-            m_ListAtLastReset.Dispose();
             m_DirtyEvents.Dispose();
         }
     }

Runtime/NetworkVariable/NetworkVariable.cs

@@ -1,7 +1,5 @@
-using UnityEngine;
 using System;
-using System.Runtime.CompilerServices;
+using UnityEngine;
-using Unity.Collections.LowLevel.Unsafe;
 
 namespace Unity.Netcode
 {
@@ -10,7 +8,7 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">the unmanaged type for <see cref="NetworkVariable{T}"/> </typeparam>
     [Serializable]
-    public class NetworkVariable<T> : NetworkVariableBase where T : unmanaged
+    public class NetworkVariable<T> : NetworkVariableBase
     {
         /// <summary>
         /// Delegate type for value changed event
@@ -52,7 +50,7 @@ namespace Unity.Netcode
             set
             {
                 // Compare bitwise
-                if (ValueEquals(ref m_InternalValue, ref value))
+                if (NetworkVariableSerialization<T>.AreEqual(ref m_InternalValue, ref value))
                 {
                     return;
                 }
@@ -66,20 +64,6 @@ namespace Unity.Netcode
             }
         }
 
-        // Compares two values of the same unmanaged type by underlying memory
-        // Ignoring any overridden value checks
-        // Size is fixed
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private static unsafe bool ValueEquals(ref T a, ref T b)
-        {
-            // get unmanaged pointers
-            var aptr = UnsafeUtility.AddressOf(ref a);
-            var bptr = UnsafeUtility.AddressOf(ref b);
-
-            // compare addresses
-            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(T)) == 0;
-        }
-
         /// <summary>
         /// Sets the <see cref="Value"/>, marks the <see cref="NetworkVariable{T}"/> dirty, and invokes the <see cref="OnValueChanged"/> callback
         /// if there are subscribers to that event.
@@ -87,7 +71,7 @@ namespace Unity.Netcode
         /// <param name="value">the new value of type `T` to be set/></param>
         private protected void Set(T value)
         {
-            m_IsDirty = true;
+            SetDirty(true);
             T previousValue = m_InternalValue;
             m_InternalValue = value;
             OnValueChanged?.Invoke(previousValue, m_InternalValue);
@@ -115,11 +99,11 @@ namespace Unity.Netcode
             // would be stored in different fields
 
             T previousValue = m_InternalValue;
-            NetworkVariableSerialization<T>.Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
 
             if (keepDirtyDelta)
             {
-                m_IsDirty = true;
+                SetDirty(true);
             }
 
             OnValueChanged?.Invoke(previousValue, m_InternalValue);
@@ -128,7 +112,7 @@ namespace Unity.Netcode
         /// <inheritdoc />
         public override void ReadField(FastBufferReader reader)
         {
-            NetworkVariableSerialization<T>.Read(reader, out m_InternalValue);
+            NetworkVariableSerialization<T>.Read(reader, ref m_InternalValue);
         }
 
         /// <inheritdoc />

Runtime/NetworkVariable/NetworkVariableBase.cs

@@ -1,4 +1,5 @@
 using System;
+using UnityEngine;
 
 namespace Unity.Netcode
 {
@@ -17,6 +18,11 @@ namespace Unity.Netcode
         /// </summary>
         private protected NetworkBehaviour m_NetworkBehaviour;
 
+        public NetworkBehaviour GetBehaviour()
+        {
+            return m_NetworkBehaviour;
+        }
+
         /// <summary>
         /// Initializes the NetworkVariable
         /// </summary>
@@ -54,7 +60,7 @@ namespace Unity.Netcode
         /// The <see cref="m_IsDirty"/> property is used to determine if the
         /// value of the `NetworkVariable` has changed.
         /// </summary>
-        private protected bool m_IsDirty;
+        private bool m_IsDirty;
 
         /// <summary>
         /// Gets or sets the name of the network variable's instance
@@ -79,6 +85,17 @@ namespace Unity.Netcode
         public virtual void SetDirty(bool isDirty)
         {
             m_IsDirty = isDirty;
+
+            if (m_IsDirty)
+            {
+                if (m_NetworkBehaviour == null)
+                {
+                    Debug.LogWarning($"NetworkVariable is written to, but doesn't know its NetworkBehaviour yet. " +
+                                     "Are you modifying a NetworkVariable before the NetworkObject is spawned?");
+                    return;
+                }
+                m_NetworkBehaviour.NetworkManager.MarkNetworkObjectDirty(m_NetworkBehaviour.NetworkObject);
+            }
         }
 
         /// <summary>
@@ -111,7 +128,7 @@ namespace Unity.Netcode
                 case NetworkVariableReadPermission.Everyone:
                     return true;
                 case NetworkVariableReadPermission.Owner:
-                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId;
+                    return clientId == m_NetworkBehaviour.NetworkObject.OwnerClientId || NetworkManager.ServerClientId == clientId;
             }
         }
 

Runtime/NetworkVariable/NetworkVariableSerialization.cs

@@ -1,6 +1,7 @@
 using System;
-using System.Collections.Generic;
 using Unity.Collections;
+using Unity.Collections.LowLevel.Unsafe;
+using UnityEditor;
 using UnityEngine;
 
 namespace Unity.Netcode
@@ -18,7 +19,97 @@ namespace Unity.Netcode
         // Taking T as an in parameter like we do in other places would require making a copy
         // of it to pass it as a ref parameter.
         public void Write(FastBufferWriter writer, ref T value);
-        public void Read(FastBufferReader reader, out T value);
+        public void Read(FastBufferReader reader, ref T value);
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class ShortSerializer : INetworkVariableSerializer<short>
+    {
+        public void Write(FastBufferWriter writer, ref short value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref short value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for shorts
+    /// </summary>
+    internal class UshortSerializer : INetworkVariableSerializer<ushort>
+    {
+        public void Write(FastBufferWriter writer, ref ushort value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ushort value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class IntSerializer : INetworkVariableSerializer<int>
+    {
+        public void Write(FastBufferWriter writer, ref int value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref int value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for ints
+    /// </summary>
+    internal class UintSerializer : INetworkVariableSerializer<uint>
+    {
+        public void Write(FastBufferWriter writer, ref uint value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref uint value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class LongSerializer : INetworkVariableSerializer<long>
+    {
+        public void Write(FastBufferWriter writer, ref long value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref long value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
+    }
+
+    /// <summary>
+    /// Packing serializer for longs
+    /// </summary>
+    internal class UlongSerializer : INetworkVariableSerializer<ulong>
+    {
+        public void Write(FastBufferWriter writer, ref ulong value)
+        {
+            BytePacker.WriteValueBitPacked(writer, value);
+        }
+        public void Read(FastBufferReader reader, ref ulong value)
+        {
+            ByteUnpacker.ReadValueBitPacked(reader, out value);
+        }
     }
 
     /// <summary>
@@ -35,79 +126,80 @@ namespace Unity.Netcode
         {
             writer.WriteUnmanagedSafe(value);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
             reader.ReadUnmanagedSafe(out value);
         }
     }
 
     /// <summary>
-    /// Serializer for FixedStrings, which does the same thing FastBufferWriter/FastBufferReader do,
+    /// Serializer for FixedStrings
-    /// but is implemented to get the data it needs using open instance delegates that are passed in
-    /// via reflection. This prevents needing T to meet any interface requirements (which isn't achievable
-    /// without incurring GC allocs on every call to Write or Read - reflection + Open Instance Delegates
-    /// circumvent that.)
-    ///
-    /// Tests show that calling these delegates doesn't cause any GC allocations even though they're
-    /// obtained via reflection and Delegate.CreateDelegate() and called on types that, at compile time,
-    /// aren't known to actually contain those methods.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    internal class FixedStringSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged
+    internal class FixedStringSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INativeList<byte>, IUTF8Bytes
     {
-        internal delegate int GetLengthDelegate(ref T value);
+        public void Write(FastBufferWriter writer, ref T value)
-        internal delegate void SetLengthDelegate(ref T value, int length);
-        internal unsafe delegate byte* GetUnsafePtrDelegate(ref T value);
-
-        internal GetLengthDelegate GetLength;
-        internal SetLengthDelegate SetLength;
-        internal GetUnsafePtrDelegate GetUnsafePtr;
-
-        public unsafe void Write(FastBufferWriter writer, ref T value)
         {
-            int length = GetLength(ref value);
+            writer.WriteValueSafe(value);
-            byte* data = GetUnsafePtr(ref value);
-            writer.WriteUnmanagedSafe(length);
-            writer.WriteBytesSafe(data, length);
         }
-        public unsafe void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
-            value = new T();
+            reader.ReadValueSafeInPlace(ref value);
-            reader.ReadValueSafe(out int length);
-            SetLength(ref value, length);
-            reader.ReadBytesSafe(GetUnsafePtr(ref value), length);
         }
     }
 
     /// <summary>
-    /// Serializer for INetworkSerializable types, which does the same thing
+    /// Serializer for unmanaged INetworkSerializable types
-    /// FastBufferWriter/FastBufferReader do, but is implemented to call the NetworkSerialize() method
-    /// via open instance delegates passed in via reflection. This prevents needing T to meet any interface
-    /// requirements (which isn't achievable without incurring GC allocs on every call to Write or Read -
-    /// reflection + Open Instance Delegates circumvent that.)
-    ///
-    /// Tests show that calling these delegates doesn't cause any GC allocations even though they're
-    /// obtained via reflection and Delegate.CreateDelegate() and called on types that, at compile time,
-    /// aren't known to actually contain those methods.
     /// </summary>
     /// <typeparam name="T"></typeparam>
-    internal class NetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged
+    internal class UnmanagedNetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : unmanaged, INetworkSerializable
     {
-        internal delegate void WriteValueDelegate(ref T value, BufferSerializer<BufferSerializerWriter> serializer);
-        internal delegate void ReadValueDelegate(ref T value, BufferSerializer<BufferSerializerReader> serializer);
-
-        internal WriteValueDelegate WriteValue;
-        internal ReadValueDelegate ReadValue;
         public void Write(FastBufferWriter writer, ref T value)
         {
             var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
-            WriteValue(ref value, bufferSerializer);
+            value.NetworkSerialize(bufferSerializer);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+            value.NetworkSerialize(bufferSerializer);
+
+        }
+    }
+
+    /// <summary>
+    /// Serializer for managed INetworkSerializable types, which differs from the unmanaged implementation in that it
+    /// has to be null-aware
+    /// <typeparam name="T"></typeparam>
+    internal class ManagedNetworkSerializableSerializer<T> : INetworkVariableSerializer<T> where T : class, INetworkSerializable, new()
+    {
+        public void Write(FastBufferWriter writer, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerWriter>(new BufferSerializerWriter(writer));
+            bool isNull = (value == null);
+            bufferSerializer.SerializeValue(ref isNull);
+            if (!isNull)
+            {
+                value.NetworkSerialize(bufferSerializer);
+            }
+        }
+        public void Read(FastBufferReader reader, ref T value)
+        {
+            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+            bool isNull = false;
+            bufferSerializer.SerializeValue(ref isNull);
+            if (isNull)
+            {
+                value = null;
+            }
+            else
+            {
+                if (value == null)
                 {
                     value = new T();
-            var bufferSerializer = new BufferSerializer<BufferSerializerReader>(new BufferSerializerReader(reader));
+                }
-            ReadValue(ref value, bufferSerializer);
+                value.NetworkSerialize(bufferSerializer);
+            }
         }
     }
 
@@ -164,7 +256,7 @@ namespace Unity.Netcode
             }
             UserNetworkVariableSerialization<T>.WriteValue(writer, value);
         }
-        public void Read(FastBufferReader reader, out T value)
+        public void Read(FastBufferReader reader, ref T value)
         {
             if (UserNetworkVariableSerialization<T>.ReadValue == null || UserNetworkVariableSerialization<T>.WriteValue == null)
             {
@@ -174,34 +266,115 @@ namespace Unity.Netcode
         }
     }
 
-    internal static class NetworkVariableSerializationTypes
+    /// <summary>
+    /// This class contains initialization functions for various different types used in NetworkVariables.
+    /// Generally speaking, these methods are called by a module initializer created by codegen (NetworkBehaviourILPP)
+    /// and do not need to be called manually.
+    ///
+    /// There are two types of initializers: Serializers and EqualityCheckers. Every type must have an EqualityChecker
+    /// registered to it in order to be used in NetworkVariable; however, not all types need a Serializer. Types without
+    /// a serializer registered will fall back to using the delegates in <see cref="UserNetworkVariableSerialization{T}"/>.
+    /// If no such delegate has been registered, a type without a serializer will throw an exception on the first attempt
+    /// to serialize or deserialize it. (Again, however, codegen handles this automatically and this registration doesn't
+    /// typically need to be performed manually.)
+    /// </summary>
+    public static class NetworkVariableSerializationTypes
     {
-        internal static readonly HashSet<Type> BaseSupportedTypes = new HashSet<Type>
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.AfterAssembliesLoaded)]
+#if UNITY_EDITOR
+        [InitializeOnLoadMethod]
+#endif
+        internal static void InitializeIntegerSerialization()
         {
-            typeof(bool),
+            NetworkVariableSerialization<short>.Serializer = new ShortSerializer();
-            typeof(byte),
+            NetworkVariableSerialization<short>.AreEqual = NetworkVariableSerialization<short>.ValueEquals;
-            typeof(sbyte),
+            NetworkVariableSerialization<ushort>.Serializer = new UshortSerializer();
-            typeof(char),
+            NetworkVariableSerialization<ushort>.AreEqual = NetworkVariableSerialization<ushort>.ValueEquals;
-            typeof(decimal),
+            NetworkVariableSerialization<int>.Serializer = new IntSerializer();
-            typeof(double),
+            NetworkVariableSerialization<int>.AreEqual = NetworkVariableSerialization<int>.ValueEquals;
-            typeof(float),
+            NetworkVariableSerialization<uint>.Serializer = new UintSerializer();
-            typeof(int),
+            NetworkVariableSerialization<uint>.AreEqual = NetworkVariableSerialization<uint>.ValueEquals;
-            typeof(uint),
+            NetworkVariableSerialization<long>.Serializer = new LongSerializer();
-            typeof(long),
+            NetworkVariableSerialization<long>.AreEqual = NetworkVariableSerialization<long>.ValueEquals;
-            typeof(ulong),
+            NetworkVariableSerialization<ulong>.Serializer = new UlongSerializer();
-            typeof(short),
+            NetworkVariableSerialization<ulong>.AreEqual = NetworkVariableSerialization<ulong>.ValueEquals;
-            typeof(ushort),
+        }
-            typeof(Vector2),
+
-            typeof(Vector3),
+        /// <summary>
-            typeof(Vector2Int),
+        /// Registeres an unmanaged type that will be serialized by a direct memcpy into a buffer
-            typeof(Vector3Int),
+        /// </summary>
-            typeof(Vector4),
+        /// <typeparam name="T"></typeparam>
-            typeof(Quaternion),
+        public static void InitializeSerializer_UnmanagedByMemcpy<T>() where T : unmanaged
-            typeof(Color),
+        {
-            typeof(Color32),
+            NetworkVariableSerialization<T>.Serializer = new UnmanagedTypeSerializer<T>();
-            typeof(Ray),
+        }
-            typeof(Ray2D)
+
-        };
+        /// <summary>
+        /// Registers an unmanaged type that implements INetworkSerializable and will be serialized through a call to
+        /// NetworkSerialize
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_UnmanagedINetworkSerializable<T>() where T : unmanaged, INetworkSerializable
+        {
+            NetworkVariableSerialization<T>.Serializer = new UnmanagedNetworkSerializableSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a managed type that implements INetworkSerializable and will be serialized through a call to
+        /// NetworkSerialize
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_ManagedINetworkSerializable<T>() where T : class, INetworkSerializable, new()
+        {
+            NetworkVariableSerialization<T>.Serializer = new ManagedNetworkSerializableSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a FixedString type that will be serialized through FastBufferReader/FastBufferWriter's FixedString
+        /// serializers
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeSerializer_FixedString<T>() where T : unmanaged, INativeList<byte>, IUTF8Bytes
+        {
+            NetworkVariableSerialization<T>.Serializer = new FixedStringSerializer<T>();
+        }
+
+        /// <summary>
+        /// Registers a managed type that will be checked for equality using T.Equals()
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_ManagedIEquatable<T>() where T : class, IEquatable<T>
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.EqualityEqualsObject;
+        }
+
+        /// <summary>
+        /// Registers an unmanaged type that will be checked for equality using T.Equals()
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_UnmanagedIEquatable<T>() where T : unmanaged, IEquatable<T>
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.EqualityEquals;
+        }
+
+        /// <summary>
+        /// Registers an unmanaged type that will be checked for equality using memcmp and only considered
+        /// equal if they are bitwise equivalent in memory
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_UnmanagedValueEquals<T>() where T : unmanaged
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.ValueEquals;
+        }
+
+        /// <summary>
+        /// Registers a managed type that will be checked for equality using the == operator
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        public static void InitializeEqualityChecker_ManagedClassEquals<T>() where T : class
+        {
+            NetworkVariableSerialization<T>.AreEqual = NetworkVariableSerialization<T>.ClassEquals;
+        }
     }
 
     /// <summary>
@@ -212,56 +385,59 @@ namespace Unity.Netcode
     /// </summary>
     /// <typeparam name="T">The type the associated NetworkVariable is templated on</typeparam>
     [Serializable]
-    public static class NetworkVariableSerialization<T> where T : unmanaged
+    public static class NetworkVariableSerialization<T>
     {
-        private static INetworkVariableSerializer<T> s_Serializer = GetSerializer();
+        internal static INetworkVariableSerializer<T> Serializer = new FallbackSerializer<T>();
 
-        private static INetworkVariableSerializer<T> GetSerializer()
+        internal delegate bool EqualsDelegate(ref T a, ref T b);
+        internal static EqualsDelegate AreEqual;
+
+        // Compares two values of the same unmanaged type by underlying memory
+        // Ignoring any overridden value checks
+        // Size is fixed
+        internal static unsafe bool ValueEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : unmanaged
         {
-            if (NetworkVariableSerializationTypes.BaseSupportedTypes.Contains(typeof(T)))
+            // get unmanaged pointers
-            {
+            var aptr = UnsafeUtility.AddressOf(ref a);
-                return new UnmanagedTypeSerializer<T>();
+            var bptr = UnsafeUtility.AddressOf(ref b);
-            }
+
-            if (typeof(INetworkSerializeByMemcpy).IsAssignableFrom(typeof(T)))
+            // compare addresses
-            {
+            return UnsafeUtility.MemCmp(aptr, bptr, sizeof(TValueType)) == 0;
-                return new UnmanagedTypeSerializer<T>();
-            }
-            if (typeof(Enum).IsAssignableFrom(typeof(T)))
-            {
-                return new UnmanagedTypeSerializer<T>();
         }
 
-            if (typeof(INetworkSerializable).IsAssignableFrom(typeof(T)))
+        internal static bool EqualityEqualsObject<TValueType>(ref TValueType a, ref TValueType b) where TValueType : class, IEquatable<TValueType>
         {
-                // Obtains "Open Instance Delegates" for the type's NetworkSerialize() methods -
+            if (a == null)
-                // one for an instance of the generic method taking BufferSerializerWriter as T,
+            {
-                // one for an instance of the generic method taking BufferSerializerReader as T
+                return b == null;
-                var writeMethod = (NetworkSerializableSerializer<T>.WriteValueDelegate)Delegate.CreateDelegate(typeof(NetworkSerializableSerializer<T>.WriteValueDelegate), null, typeof(T).GetMethod(nameof(INetworkSerializable.NetworkSerialize)).MakeGenericMethod(typeof(BufferSerializerWriter)));
-                var readMethod = (NetworkSerializableSerializer<T>.ReadValueDelegate)Delegate.CreateDelegate(typeof(NetworkSerializableSerializer<T>.ReadValueDelegate), null, typeof(T).GetMethod(nameof(INetworkSerializable.NetworkSerialize)).MakeGenericMethod(typeof(BufferSerializerReader)));
-                return new NetworkSerializableSerializer<T> { WriteValue = writeMethod, ReadValue = readMethod };
             }
 
-            if (typeof(IUTF8Bytes).IsAssignableFrom(typeof(T)) && typeof(INativeList<byte>).IsAssignableFrom(typeof(T)))
+            if (b == null)
             {
-                // Get "OpenInstanceDelegates" for the Length property (get and set, which are prefixed
+                return false;
-                // with "get_" and "set_" under the hood and emitted as methods) and GetUnsafePtr()
-                var getLength = (FixedStringSerializer<T>.GetLengthDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.GetLengthDelegate), null, typeof(T).GetMethod("get_" + nameof(INativeList<byte>.Length)));
-                var setLength = (FixedStringSerializer<T>.SetLengthDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.SetLengthDelegate), null, typeof(T).GetMethod("set_" + nameof(INativeList<byte>.Length)));
-                var getUnsafePtr = (FixedStringSerializer<T>.GetUnsafePtrDelegate)Delegate.CreateDelegate(typeof(FixedStringSerializer<T>.GetUnsafePtrDelegate), null, typeof(T).GetMethod(nameof(IUTF8Bytes.GetUnsafePtr)));
-                return new FixedStringSerializer<T> { GetLength = getLength, SetLength = setLength, GetUnsafePtr = getUnsafePtr };
             }
 
-            return new FallbackSerializer<T>();
+            return a.Equals(b);
+        }
+
+        internal static bool EqualityEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : unmanaged, IEquatable<TValueType>
+        {
+            return a.Equals(b);
+        }
+
+        internal static bool ClassEquals<TValueType>(ref TValueType a, ref TValueType b) where TValueType : class
+        {
+            return a == b;
         }
 
         internal static void Write(FastBufferWriter writer, ref T value)
         {
-            s_Serializer.Write(writer, ref value);
+            Serializer.Write(writer, ref value);
         }
 
-        internal static void Read(FastBufferReader reader, out T value)
+        internal static void Read(FastBufferReader reader, ref T value)
         {
-            s_Serializer.Read(reader, out value);
+            Serializer.Read(reader, ref value);
         }
     }
 }

Runtime/SceneManagement/DefaultSceneManagerHandler.cs

@@ -0,0 +1,377 @@
+using System;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+
+
+namespace Unity.Netcode
+{
+    /// <summary>
+    ///  The default SceneManagerHandler that interfaces between the SceneManager and NetworkSceneManager
+    /// </summary>
+    internal class DefaultSceneManagerHandler : ISceneManagerHandler
+    {
+        private Scene m_InvalidScene = new Scene();
+
+        internal struct SceneEntry
+        {
+            public bool IsAssigned;
+            public Scene Scene;
+        }
+
+        internal Dictionary<string, Dictionary<int, SceneEntry>> SceneNameToSceneHandles = new Dictionary<string, Dictionary<int, SceneEntry>>();
+
+        public AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventProgress sceneEventProgress)
+        {
+            var operation = SceneManager.LoadSceneAsync(sceneName, loadSceneMode);
+            sceneEventProgress.SetAsyncOperation(operation);
+            return operation;
+        }
+
+        public AsyncOperation UnloadSceneAsync(Scene scene, SceneEventProgress sceneEventProgress)
+        {
+            var operation = SceneManager.UnloadSceneAsync(scene);
+            sceneEventProgress.SetAsyncOperation(operation);
+            return operation;
+        }
+
+        /// <summary>
+        /// Resets scene tracking
+        /// </summary>
+        public void ClearSceneTracking(NetworkManager networkManager)
+        {
+            SceneNameToSceneHandles.Clear();
+        }
+
+        /// <summary>
+        /// Stops tracking a specific scene
+        /// </summary>
+        public void StopTrackingScene(int handle, string name, NetworkManager networkManager)
+        {
+            if (SceneNameToSceneHandles.ContainsKey(name))
+            {
+                if (SceneNameToSceneHandles[name].ContainsKey(handle))
+                {
+                    SceneNameToSceneHandles[name].Remove(handle);
+                    if (SceneNameToSceneHandles[name].Count == 0)
+                    {
+                        SceneNameToSceneHandles.Remove(name);
+                    }
+                }
+            }
+        }
+
+        /// <summary>
+        /// Starts tracking a specific scene
+        /// </summary>
+        public void StartTrackingScene(Scene scene, bool assigned, NetworkManager networkManager)
+        {
+            if (!SceneNameToSceneHandles.ContainsKey(scene.name))
+            {
+                SceneNameToSceneHandles.Add(scene.name, new Dictionary<int, SceneEntry>());
+            }
+
+            if (!SceneNameToSceneHandles[scene.name].ContainsKey(scene.handle))
+            {
+                var sceneEntry = new SceneEntry()
+                {
+                    IsAssigned = true,
+                    Scene = scene
+                };
+                SceneNameToSceneHandles[scene.name].Add(scene.handle, sceneEntry);
+            }
+            else
+            {
+                throw new Exception($"[Duplicate Handle] Scene {scene.name} already has scene handle {scene.handle} registered!");
+            }
+        }
+
+        /// <summary>
+        /// Determines if there is an existing scene loaded that matches the scene name but has not been assigned
+        /// </summary>
+        public bool DoesSceneHaveUnassignedEntry(string sceneName, NetworkManager networkManager)
+        {
+            var scenesWithSceneName = new List<Scene>();
+
+            // Get all loaded scenes with the same name
+            for (int i = 0; i < SceneManager.sceneCount; i++)
+            {
+                var scene = SceneManager.GetSceneAt(i);
+                if (scene.name == sceneName)
+                {
+                    scenesWithSceneName.Add(scene);
+                }
+            }
+
+            // If there are no scenes of this name loaded then we have no loaded scenes
+            // to use
+            if (scenesWithSceneName.Count == 0)
+            {
+                return false;
+            }
+
+            // If we have 1 or more scenes with the name and we have no entries, then we do have
+            // a scene to use
+            if (scenesWithSceneName.Count > 0 && !SceneNameToSceneHandles.ContainsKey(sceneName))
+            {
+                return true;
+            }
+
+            // Determine if any of the loaded scenes has been used for synchronizing
+            foreach (var scene in scenesWithSceneName)
+            {
+                // If we don't have the handle, then we can use that scene
+                if (!SceneNameToSceneHandles[scene.name].ContainsKey(scene.handle))
+                {
+                    return true;
+                }
+
+                // If we have an entry, but it is not yet assigned (i.e. preloaded)
+                // then we can use that.
+                if (!SceneNameToSceneHandles[scene.name][scene.handle].IsAssigned)
+                {
+                    return true;
+                }
+            }
+            // If none were found, then we have no available scene (which most likely means one will get loaded)
+            return false;
+        }
+
+        /// <summary>
+        /// This will find any scene entry that hasn't been used/assigned, set the entry to assigned, and
+        /// return the associated scene. If none are found it returns an invalid scene.
+        /// </summary>
+        public Scene GetSceneFromLoadedScenes(string sceneName, NetworkManager networkManager)
+        {
+            if (SceneNameToSceneHandles.ContainsKey(sceneName))
+            {
+                foreach (var sceneHandleEntry in SceneNameToSceneHandles[sceneName])
+                {
+                    if (!sceneHandleEntry.Value.IsAssigned)
+                    {
+                        var sceneEntry = sceneHandleEntry.Value;
+                        sceneEntry.IsAssigned = true;
+                        SceneNameToSceneHandles[sceneName][sceneHandleEntry.Key] = sceneEntry;
+                        return sceneEntry.Scene;
+                    }
+                }
+            }
+            // If we found nothing return an invalid scene
+            return m_InvalidScene;
+        }
+
+        /// <summary>
+        /// Only invoked is client synchronization is additive, this will generate the scene tracking table
+        /// in order to re-use the same scenes the server is synchronizing instead of having to unload the
+        /// scenes and reload them when synchronizing (i.e. client disconnects due to external reason, the
+        /// same application instance is still running, the same scenes are still loaded on the client, and
+        /// upon reconnecting the client doesn't have to unload the scenes and then reload them)
+        /// </summary>
+        public void PopulateLoadedScenes(ref Dictionary<int, Scene> scenesLoaded, NetworkManager networkManager)
+        {
+            SceneNameToSceneHandles.Clear();
+            var sceneCount = SceneManager.sceneCount;
+            for (int i = 0; i < sceneCount; i++)
+            {
+                var scene = SceneManager.GetSceneAt(i);
+                if (!SceneNameToSceneHandles.ContainsKey(scene.name))
+                {
+                    SceneNameToSceneHandles.Add(scene.name, new Dictionary<int, SceneEntry>());
+                }
+
+                if (!SceneNameToSceneHandles[scene.name].ContainsKey(scene.handle))
+                {
+                    var sceneEntry = new SceneEntry()
+                    {
+                        IsAssigned = false,
+                        Scene = scene
+                    };
+                    SceneNameToSceneHandles[scene.name].Add(scene.handle, sceneEntry);
+                    if (!scenesLoaded.ContainsKey(scene.handle))
+                    {
+                        scenesLoaded.Add(scene.handle, scene);
+                    }
+                }
+                else
+                {
+                    throw new Exception($"[Duplicate Handle] Scene {scene.name} already has scene handle {scene.handle} registered!");
+                }
+            }
+        }
+
+        private List<Scene> m_ScenesToUnload = new List<Scene>();
+
+        /// <summary>
+        /// Unloads any scenes that have not been assigned.
+        /// </summary>
+        /// <param name="networkManager"></param>
+        public void UnloadUnassignedScenes(NetworkManager networkManager = null)
+        {
+            var sceneManager = networkManager.SceneManager;
+            SceneManager.sceneUnloaded += SceneManager_SceneUnloaded;
+            foreach (var sceneEntry in SceneNameToSceneHandles)
+            {
+                var scenHandleEntries = SceneNameToSceneHandles[sceneEntry.Key];
+                foreach (var sceneHandleEntry in scenHandleEntries)
+                {
+                    if (!sceneHandleEntry.Value.IsAssigned)
+                    {
+                        if (sceneManager.VerifySceneBeforeUnloading == null || sceneManager.VerifySceneBeforeUnloading.Invoke(sceneHandleEntry.Value.Scene))
+                        {
+                            m_ScenesToUnload.Add(sceneHandleEntry.Value.Scene);
+                        }
+                    }
+                }
+            }
+            foreach (var sceneToUnload in m_ScenesToUnload)
+            {
+                SceneManager.UnloadSceneAsync(sceneToUnload);
+            }
+        }
+
+        private void SceneManager_SceneUnloaded(Scene scene)
+        {
+            if (SceneNameToSceneHandles.ContainsKey(scene.name))
+            {
+                if (SceneNameToSceneHandles[scene.name].ContainsKey(scene.handle))
+                {
+                    SceneNameToSceneHandles[scene.name].Remove(scene.handle);
+                }
+                if (SceneNameToSceneHandles[scene.name].Count == 0)
+                {
+                    SceneNameToSceneHandles.Remove(scene.name);
+                }
+                m_ScenesToUnload.Remove(scene);
+                if (m_ScenesToUnload.Count == 0)
+                {
+                    SceneManager.sceneUnloaded -= SceneManager_SceneUnloaded;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Handles determining if a client should attempt to load a scene during synchronization.
+        /// </summary>
+        /// <param name="sceneName">name of the scene to be loaded</param>
+        /// <param name="isPrimaryScene">when in client synchronization mode single, this determines if the scene is the primary active scene</param>
+        /// <param name="clientSynchronizationMode">the current client synchronization mode</param>
+        /// <param name="networkManager"><see cref="NetworkManager"/> instance</param>
+        /// <returns></returns>
+        public bool ClientShouldPassThrough(string sceneName, bool isPrimaryScene, LoadSceneMode clientSynchronizationMode, NetworkManager networkManager)
+        {
+            var shouldPassThrough = clientSynchronizationMode == LoadSceneMode.Single ? false : DoesSceneHaveUnassignedEntry(sceneName, networkManager);
+            var activeScene = SceneManager.GetActiveScene();
+
+            // If shouldPassThrough is not yet true and the scene to be loaded is the currently active scene
+            if (!shouldPassThrough && sceneName == activeScene.name)
+            {
+                // In additive mode we always pass through, but in LoadSceneMode.Single we only pass through if the currently active scene
+                // is the primary scene to be loaded
+                if (clientSynchronizationMode == LoadSceneMode.Additive || (isPrimaryScene && clientSynchronizationMode == LoadSceneMode.Single))
+                {
+                    // don't try to reload this scene and pass through to post load processing.
+                    shouldPassThrough = true;
+                }
+            }
+            return shouldPassThrough;
+        }
+
+        /// <summary>
+        /// Handles migrating dynamically spawned NetworkObjects to the DDOL when a scene is unloaded
+        /// </summary>
+        /// <param name="networkManager"><see cref="NetworkManager"/>relative instance</param>
+        /// <param name="scene">scene being unloaded</param>
+        public void MoveObjectsFromSceneToDontDestroyOnLoad(ref NetworkManager networkManager, Scene scene)
+        {
+            bool isActiveScene = scene == SceneManager.GetActiveScene();
+            // Create a local copy of the spawned objects list since the spawn manager will adjust the list as objects
+            // are despawned.
+            var localSpawnedObjectsHashSet = new HashSet<NetworkObject>(networkManager.SpawnManager.SpawnedObjectsList);
+            foreach (var networkObject in localSpawnedObjectsHashSet)
+            {
+                if (networkObject == null || (networkObject != null && networkObject.gameObject.scene.handle != scene.handle))
+                {
+                    continue;
+                }
+
+                // Only NetworkObjects marked to not be destroyed with the scene and are not already in the DDOL are preserved
+                if (!networkObject.DestroyWithScene && networkObject.gameObject.scene != networkManager.SceneManager.DontDestroyOnLoadScene)
+                {
+                    // Only move dynamically spawned NetworkObjects with no parent as the children will follow
+                    if (networkObject.gameObject.transform.parent == null && networkObject.IsSceneObject != null && !networkObject.IsSceneObject.Value)
+                    {
+                        UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
+                    }
+                }
+                else if (networkManager.IsServer)
+                {
+                    networkObject.Despawn();
+                }
+                else // We are a client, migrate the object into the DDOL temporarily until it receives the destroy command from the server
+                {
+                    UnityEngine.Object.DontDestroyOnLoad(networkObject.gameObject);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Sets the client synchronization mode which impacts whether both the server or client take into consideration scenes loaded before
+        /// starting the <see cref="NetworkManager"/>.
+        /// </summary>
+        /// <remarks>
+        /// <see cref="LoadSceneMode.Single"/>: Does not take preloaded scenes into consideration
+        /// <see cref="LoadSceneMode.Single"/>: Does take preloaded scenes into consideration
+        /// </remarks>
+        /// <param name="networkManager">relative <see cref="NetworkManager"/> instance</param>
+        /// <param name="mode"><see cref="LoadSceneMode.Single"/> or <see cref="LoadSceneMode.Additive"/></param>
+        public void SetClientSynchronizationMode(ref NetworkManager networkManager, LoadSceneMode mode)
+        {
+            var sceneManager = networkManager.SceneManager;
+            // Don't let client's set this value
+            if (!networkManager.IsServer)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                {
+                    NetworkLog.LogWarning("Clients should not set this value as it is automatically synchronized with the server's setting!");
+                }
+                return;
+            }
+            else // Warn users if they are changing this after there are clients already connected and synchronized
+            if (networkManager.ConnectedClientsIds.Count > (networkManager.IsServer ? 0 : 1) && sceneManager.ClientSynchronizationMode != mode)
+            {
+                if (NetworkLog.CurrentLogLevel <= LogLevel.Normal)
+                {
+                    NetworkLog.LogWarning("Server is changing client synchronization mode after clients have been synchronized! It is recommended to do this before clients are connected!");
+                }
+            }
+
+            // For additive client synchronization, we take into consideration scenes
+            // already loaded.
+            if (mode == LoadSceneMode.Additive)
+            {
+                for (int i = 0; i < SceneManager.sceneCount; i++)
+                {
+                    var scene = SceneManager.GetSceneAt(i);
+
+                    // If using scene verification
+                    if (sceneManager.VerifySceneBeforeLoading != null)
+                    {
+                        // Determine if we should take this scene into consideration
+                        if (!sceneManager.VerifySceneBeforeLoading.Invoke(scene.buildIndex, scene.name, LoadSceneMode.Additive))
+                        {
+                            continue;
+                        }
+                    }
+
+                    // If the scene is not already in the ScenesLoaded list, then add it
+                    if (!sceneManager.ScenesLoaded.ContainsKey(scene.handle))
+                    {
+                        sceneManager.ScenesLoaded.Add(scene.handle, scene);
+                    }
+                }
+            }
+            // Set the client synchronization mode
+            sceneManager.ClientSynchronizationMode = mode;
+        }
+    }
+}

Runtime/SceneManagement/DefaultSceneManagerHandler.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 8c18076bb9734cf4ea7297f85b7729be
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Runtime/SceneManagement/ISceneManagerHandler.cs

@@ -1,4 +1,4 @@
-using System;
+using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
@@ -10,25 +10,27 @@ namespace Unity.Netcode
     /// </summary>
     internal interface ISceneManagerHandler
     {
-        // Generic action to call when a scene is finished loading/unloading
+        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventProgress sceneEventProgress);
-        struct SceneEventAction
-        {
-            internal uint SceneEventId;
-            internal Action<uint> EventAction;
-            /// <summary>
-            /// Used server-side for integration testing in order to
-            /// invoke the SceneEventProgress once done loading
-            /// </summary>
-            internal Action Completed;
-            internal void Invoke()
-            {
-                Completed?.Invoke();
-                EventAction.Invoke(SceneEventId);
-            }
-        }
 
-        AsyncOperation LoadSceneAsync(string sceneName, LoadSceneMode loadSceneMode, SceneEventAction sceneEventAction);
+        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventProgress sceneEventProgress);
 
-        AsyncOperation UnloadSceneAsync(Scene scene, SceneEventAction sceneEventAction);
+        void PopulateLoadedScenes(ref Dictionary<int, Scene> scenesLoaded, NetworkManager networkManager = null);
+        Scene GetSceneFromLoadedScenes(string sceneName, NetworkManager networkManager = null);
+
+        bool DoesSceneHaveUnassignedEntry(string sceneName, NetworkManager networkManager = null);
+
+        void StopTrackingScene(int handle, string name, NetworkManager networkManager = null);
+
+        void StartTrackingScene(Scene scene, bool assigned, NetworkManager networkManager = null);
+
+        void ClearSceneTracking(NetworkManager networkManager = null);
+
+        void UnloadUnassignedScenes(NetworkManager networkManager = null);
+
+        void MoveObjectsFromSceneToDontDestroyOnLoad(ref NetworkManager networkManager, Scene scene);
+
+        void SetClientSynchronizationMode(ref NetworkManager networkManager, LoadSceneMode mode);
+
+        bool ClientShouldPassThrough(string sceneName, bool isPrimaryScene, LoadSceneMode clientSynchronizationMode, NetworkManager networkManager);
     }
 }

Runtime/SceneManagement/SceneEventData.cs

@@ -1,5 +1,5 @@
-using System.Collections.Generic;
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using Unity.Collections;
 using UnityEngine.SceneManagement;
@@ -80,6 +80,16 @@ namespace Unity.Netcode
         /// <b>Event Notification:</b> Both server and client receive a local notification.
         /// </summary>
         SynchronizeComplete,
+        /// <summary>
+        /// Synchronizes clients when the active scene has changed
+        /// See: <see cref="NetworkObject.ActiveSceneSynchronization"/>
+        /// </summary>
+        ActiveSceneChanged,
+        /// <summary>
+        /// Synchronizes clients when one or more NetworkObjects are migrated into a new scene
+        /// See: <see cref="NetworkObject.SceneMigrationSynchronization"/>
+        /// </summary>
+        ObjectSceneChanged,
     }
 
     /// <summary>
@@ -94,7 +104,7 @@ namespace Unity.Netcode
         internal ForceNetworkSerializeByMemcpy<Guid> SceneEventProgressId;
         internal uint SceneEventId;
 
-
+        internal uint ActiveSceneHash;
         internal uint SceneHash;
         internal int SceneHandle;
 
@@ -139,6 +149,8 @@ namespace Unity.Netcode
         internal Queue<uint> ScenesToSynchronize;
         internal Queue<uint> SceneHandlesToSynchronize;
 
+        internal LoadSceneMode ClientSynchronizationMode;
+
 
         /// <summary>
         /// Server Side:
@@ -243,13 +255,38 @@ namespace Unity.Netcode
                     m_NetworkObjectsSync.Add(sobj);
                 }
             }
+
+            // Sort by parents before children
+            m_NetworkObjectsSync.Sort(SortParentedNetworkObjects);
+
+            // Sort by INetworkPrefabInstanceHandler implementation before the
+            // NetworkObjects spawned by the implementation
             m_NetworkObjectsSync.Sort(SortNetworkObjects);
+
+            // This is useful to know what NetworkObjects a client is going to be synchronized with
+            // as well as the order in which they will be deserialized
+            if (m_NetworkManager.LogLevel == LogLevel.Developer)
+            {
+                var messageBuilder = new System.Text.StringBuilder(0xFFFF);
+                messageBuilder.Append("[Server-Side Client-Synchronization] NetworkObject serialization order:");
+                foreach (var networkObject in m_NetworkObjectsSync)
+                {
+                    messageBuilder.Append($"{networkObject.name}");
+                }
+                NetworkLog.LogInfo(messageBuilder.ToString());
+            }
         }
 
         internal void AddDespawnedInSceneNetworkObjects()
         {
             m_DespawnedInSceneObjectsSync.Clear();
-            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) => c.NetworkManager == m_NetworkManager);
+            // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) => c.NetworkManager == m_NetworkManager);
+#else
+            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) => c.NetworkManager == m_NetworkManager);
+
+#endif
             foreach (var sobj in inSceneNetworkObjects)
             {
                 if (sobj.IsSceneObject.HasValue && sobj.IsSceneObject.Value && !sobj.IsSpawned)
@@ -290,6 +327,8 @@ namespace Unity.Netcode
                 case SceneEventType.ReSynchronize:
                 case SceneEventType.LoadEventCompleted:
                 case SceneEventType.UnloadEventCompleted:
+                case SceneEventType.ActiveSceneChanged:
+                case SceneEventType.ObjectSceneChanged:
                     {
                         return true;
                     }
@@ -323,6 +362,32 @@ namespace Unity.Netcode
             return 0;
         }
 
+        /// <summary>
+        /// Sorts the synchronization order of the NetworkObjects to be serialized
+        /// by parents before children.
+        /// </summary>
+        /// <remarks>
+        /// This only handles late joining players. Spawning and nesting several children
+        /// dynamically is still handled by the orphaned child list when deserialized out of
+        /// hierarchical order (i.e. Spawn parent and child dynamically, parent message is
+        /// dropped and re-sent but child object is received and processed)
+        /// </remarks>
+        private int SortParentedNetworkObjects(NetworkObject first, NetworkObject second)
+        {
+            // If the first has a parent, move the first down
+            if (first.transform.parent != null)
+            {
+                return 1;
+            }
+            else // If the second has a parent and the first does not, then move the first up
+            if (second.transform.parent != null)
+            {
+                return -1;
+            }
+            return 0;
+        }
+
+
         /// <summary>
         /// Client and Server Side:
         /// Serializes data based on the SceneEvent type (<see cref="SceneEventType"/>)
@@ -333,14 +398,30 @@ namespace Unity.Netcode
             // Write the scene event type
             writer.WriteValueSafe(SceneEventType);
 
+            if (SceneEventType == SceneEventType.ActiveSceneChanged)
+            {
+                writer.WriteValueSafe(ActiveSceneHash);
+                return;
+            }
+
+            if (SceneEventType == SceneEventType.ObjectSceneChanged)
+            {
+                SerializeObjectsMovedIntoNewScene(writer);
+                return;
+            }
+
             // Write the scene loading mode
-            writer.WriteValueSafe(LoadSceneMode);
+            writer.WriteValueSafe((byte)LoadSceneMode);
 
             // Write the scene event progress Guid
             if (SceneEventType != SceneEventType.Synchronize)
             {
                 writer.WriteValueSafe(SceneEventProgressId);
             }
+            else
+            {
+                writer.WriteValueSafe(ClientSynchronizationMode);
+            }
 
             // Write the scene index and handle
             writer.WriteValueSafe(SceneHash);
@@ -350,6 +431,7 @@ namespace Unity.Netcode
             {
                 case SceneEventType.Synchronize:
                     {
+                        writer.WriteValueSafe(ActiveSceneHash);
                         WriteSceneSynchronizationData(writer);
                         break;
                     }
@@ -394,33 +476,32 @@ namespace Unity.Netcode
             // Size Place Holder -- Start
             // !!NOTE!!: Since this is a placeholder to be set after we know how much we have written,
             // for stream offset purposes this MUST not be a packed value!
-            writer.WriteValueSafe((int)0);
+            writer.WriteValueSafe(0);
             int totalBytes = 0;
 
             // Write the number of NetworkObjects we are serializing
-            BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync.Count());
+            writer.WriteValueSafe(m_NetworkObjectsSync.Count);
+
             // Serialize all NetworkObjects that are spawned
-            for (var i = 0; i < m_NetworkObjectsSync.Count(); ++i)
+            for (var i = 0; i < m_NetworkObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
                 var sceneObject = m_NetworkObjectsSync[i].GetMessageSceneObject(TargetClientId);
-                BytePacker.WriteValuePacked(writer, m_NetworkObjectsSync[i].GetSceneOriginHandle());
                 sceneObject.Serialize(writer);
                 var noStop = writer.Position;
-                totalBytes += (int)(noStop - noStart);
+                totalBytes += noStop - noStart;
             }
 
             // Write the number of despawned in-scene placed NetworkObjects
-            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count());
+            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count);
             // Write the scene handle and GlobalObjectIdHash value
-            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count(); ++i)
+            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
             {
                 var noStart = writer.Position;
-                var sceneObject = m_DespawnedInSceneObjectsSync[i].GetMessageSceneObject(TargetClientId);
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
-                BytePacker.WriteValuePacked(writer, m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
                 var noStop = writer.Position;
-                totalBytes += (int)(noStop - noStart);
+                totalBytes += noStop - noStart;
             }
 
             // Size Place Holder -- End
@@ -452,8 +533,6 @@ namespace Unity.Netcode
                 {
                     if (keyValuePairBySceneHandle.Value.Observers.Contains(TargetClientId))
                     {
-                        // Write our server relative scene handle for the NetworkObject being serialized
-                        writer.WriteValueSafe(keyValuePairBySceneHandle.Key);
                         // Serialize the NetworkObject
                         var sceneObject = keyValuePairBySceneHandle.Value.GetMessageSceneObject(TargetClientId);
                         sceneObject.Serialize(writer);
@@ -462,6 +541,15 @@ namespace Unity.Netcode
                 }
             }
 
+            // Write the number of despawned in-scene placed NetworkObjects
+            writer.WriteValueSafe(m_DespawnedInSceneObjectsSync.Count);
+            // Write the scene handle and GlobalObjectIdHash value
+            for (var i = 0; i < m_DespawnedInSceneObjectsSync.Count; ++i)
+            {
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GetSceneOriginHandle());
+                writer.WriteValueSafe(m_DespawnedInSceneObjectsSync[i].GlobalObjectIdHash);
+            }
+
             var tailPosition = writer.Position;
             // Reposition to our count position to the head before we wrote our object count
             writer.Seek(headPosition);
@@ -479,12 +567,37 @@ namespace Unity.Netcode
         internal void Deserialize(FastBufferReader reader)
         {
             reader.ReadValueSafe(out SceneEventType);
-            reader.ReadValueSafe(out LoadSceneMode);
+            if (SceneEventType == SceneEventType.ActiveSceneChanged)
+            {
+                reader.ReadValueSafe(out ActiveSceneHash);
+                return;
+            }
+
+            if (SceneEventType == SceneEventType.ObjectSceneChanged)
+            {
+                // Defer these scene event types if a client hasn't finished synchronizing
+                if (!m_NetworkManager.IsConnectedClient)
+                {
+                    DeferObjectsMovedIntoNewScene(reader);
+                }
+                else
+                {
+                    DeserializeObjectsMovedIntoNewScene(reader);
+                }
+                return;
+            }
+
+            reader.ReadValueSafe(out byte loadSceneMode);
+            LoadSceneMode = (LoadSceneMode)loadSceneMode;
 
             if (SceneEventType != SceneEventType.Synchronize)
             {
                 reader.ReadValueSafe(out SceneEventProgressId);
             }
+            else
+            {
+                reader.ReadValueSafe(out ClientSynchronizationMode);
+            }
 
             reader.ReadValueSafe(out SceneHash);
             reader.ReadValueSafe(out SceneHandle);
@@ -493,6 +606,7 @@ namespace Unity.Netcode
             {
                 case SceneEventType.Synchronize:
                     {
+                        reader.ReadValueSafe(out ActiveSceneHash);
                         CopySceneSynchronizationData(reader);
                         break;
                     }
@@ -570,15 +684,19 @@ namespace Unity.Netcode
 
                 for (ushort i = 0; i < newObjectsCount; i++)
                 {
-                    InternalBuffer.ReadValueSafe(out int sceneHandle);
-                    // Set our relative scene to the NetworkObject
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneHandle);
-
-                    // Deserialize the NetworkObject
                     var sceneObject = new NetworkObject.SceneObject();
                     sceneObject.Deserialize(InternalBuffer);
+
+                    if (sceneObject.IsSceneObject)
+                    {
+                        // Set our relative scene to the NetworkObject
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
+
                     NetworkObject.AddSceneObject(sceneObject, InternalBuffer, m_NetworkManager);
                 }
+                // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
+                DeserializeDespawnedInScenePlacedNetworkObjects();
             }
             finally
             {
@@ -600,7 +718,11 @@ namespace Unity.Netcode
 
             if (networkObjectsToRemove.Length > 0)
             {
+#if UNITY_2023_1_OR_NEWER
+                var networkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsSortMode.InstanceID);
+#else
                 var networkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>();
+#endif
                 var networkObjectIdToNetworkObject = new Dictionary<ulong, NetworkObject>();
                 foreach (var networkObject in networkObjects)
                 {
@@ -702,38 +824,11 @@ namespace Unity.Netcode
         }
 
         /// <summary>
-        /// Client Side:
+        /// For synchronizing any despawned in-scene placed NetworkObjects that were
-        /// During the processing of a server sent Event_Sync, this method will be called for each scene once
+        /// despawned by the server during synchronization or scene loading
-        /// it is finished loading.  The client will also build a list of NetworkObjects that it spawned during
-        /// this process which will be used as part of the Event_Sync_Complete response.
         /// </summary>
-        /// <param name="networkManager"></param>
+        private void DeserializeDespawnedInScenePlacedNetworkObjects()
-        internal void SynchronizeSceneNetworkObjects(NetworkManager networkManager)
         {
-            try
-            {
-                // Process all spawned NetworkObjects for this network session
-                ByteUnpacker.ReadValuePacked(InternalBuffer, out int newObjectsCount);
-
-
-                for (int i = 0; i < newObjectsCount; i++)
-                {
-                    // We want to make sure for each NetworkObject we have the appropriate scene selected as the scene that is
-                    // currently being synchronized.  This assures in-scene placed NetworkObjects will use the right NetworkObject
-                    // from the list of populated <see cref="NetworkSceneManager.ScenePlacedObjects"/>
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out int handle);
-                    m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(handle);
-
-                    var sceneObject = new NetworkObject.SceneObject();
-                    sceneObject.Deserialize(InternalBuffer);
-
-                    var spawnedNetworkObject = NetworkObject.AddSceneObject(sceneObject, InternalBuffer, networkManager);
-                    if (!m_NetworkObjectsSync.Contains(spawnedNetworkObject))
-                    {
-                        m_NetworkObjectsSync.Add(spawnedNetworkObject);
-                    }
-                }
-
             // Process all de-spawned in-scene NetworkObjects for this network session
             m_DespawnedInSceneObjects.Clear();
             InternalBuffer.ReadValueSafe(out int despawnedObjectsCount);
@@ -742,8 +837,8 @@ namespace Unity.Netcode
             for (int i = 0; i < despawnedObjectsCount; i++)
             {
                 // We just need to get the scene
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out int networkSceneHandle);
+                InternalBuffer.ReadValueSafe(out int networkSceneHandle);
-                    ByteUnpacker.ReadValuePacked(InternalBuffer, out uint globalObjectIdHash);
+                InternalBuffer.ReadValueSafe(out uint globalObjectIdHash);
                 var sceneRelativeNetworkObjects = new Dictionary<uint, NetworkObject>();
                 if (!sceneCache.ContainsKey(networkSceneHandle))
                 {
@@ -753,13 +848,24 @@ namespace Unity.Netcode
                         if (m_NetworkManager.SceneManager.ScenesLoaded.ContainsKey(localSceneHandle))
                         {
                             var objectRelativeScene = m_NetworkManager.SceneManager.ScenesLoaded[localSceneHandle];
-                                var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>().Where((c) =>
+
+                            // Find all active and non-active in-scene placed NetworkObjects
+#if UNITY_2023_1_OR_NEWER
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsByType<NetworkObject>(UnityEngine.FindObjectsInactive.Include, UnityEngine.FindObjectsSortMode.InstanceID).Where((c) =>
                             c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#else
+                            var inSceneNetworkObjects = UnityEngine.Object.FindObjectsOfType<NetworkObject>(includeInactive: true).Where((c) =>
+                            c.GetSceneOriginHandle() == localSceneHandle && (c.IsSceneObject != false)).ToList();
+#endif
+
 
                             foreach (var inSceneObject in inSceneNetworkObjects)
+                            {
+                                if (!sceneRelativeNetworkObjects.ContainsKey(inSceneObject.GlobalObjectIdHash))
                                 {
                                     sceneRelativeNetworkObjects.Add(inSceneObject.GlobalObjectIdHash, inSceneObject);
                                 }
+                            }
                             // Add this to a cache so we don't have to run this potentially multiple times (nothing will spawn or despawn during this time
                             sceneCache.Add(networkSceneHandle, sceneRelativeNetworkObjects);
                         }
@@ -793,7 +899,6 @@ namespace Unity.Netcode
                     {
                         m_NetworkManager.SceneManager.ScenePlacedObjects[globalObjectIdHash].Add(sceneRelativeNetworkObjects[globalObjectIdHash].GetSceneOriginHandle(), sceneRelativeNetworkObjects[globalObjectIdHash]);
                     }
-
                 }
                 else
                 {
@@ -801,6 +906,46 @@ namespace Unity.Netcode
                 }
             }
         }
+
+        /// <summary>
+        /// Client Side:
+        /// During the processing of a server sent Event_Sync, this method will be called for each scene once
+        /// it is finished loading.  The client will also build a list of NetworkObjects that it spawned during
+        /// this process which will be used as part of the Event_Sync_Complete response.
+        /// </summary>
+        /// <param name="networkManager"></param>
+        internal void SynchronizeSceneNetworkObjects(NetworkManager networkManager)
+        {
+            try
+            {
+                // Process all spawned NetworkObjects for this network session
+                InternalBuffer.ReadValueSafe(out int newObjectsCount);
+                for (int i = 0; i < newObjectsCount; i++)
+                {
+                    var sceneObject = new NetworkObject.SceneObject();
+                    sceneObject.Deserialize(InternalBuffer);
+
+                    // If the sceneObject is in-scene placed, then set the scene being synchronized
+                    if (sceneObject.IsSceneObject)
+                    {
+                        m_NetworkManager.SceneManager.SetTheSceneBeingSynchronized(sceneObject.NetworkSceneHandle);
+                    }
+                    var spawnedNetworkObject = NetworkObject.AddSceneObject(sceneObject, InternalBuffer, networkManager);
+
+                    // If we failed to deserialize the NetowrkObject then don't add null to the list
+                    if (spawnedNetworkObject != null)
+                    {
+                        if (!m_NetworkObjectsSync.Contains(spawnedNetworkObject))
+                        {
+                            m_NetworkObjectsSync.Add(spawnedNetworkObject);
+                        }
+                    }
+                }
+
+                // Now deserialize the despawned in-scene placed NetworkObjects list (if any)
+                DeserializeDespawnedInScenePlacedNetworkObjects();
+
+            }
             finally
             {
                 InternalBuffer.Dispose();
@@ -850,6 +995,143 @@ namespace Unity.Netcode
             }
         }
 
+        /// <summary>
+        /// Serialize scene handles and associated NetworkObjects that were migrated
+        /// into a new scene.
+        /// </summary>
+        private void SerializeObjectsMovedIntoNewScene(FastBufferWriter writer)
+        {
+            var sceneManager = m_NetworkManager.SceneManager;
+            // Write the number of scene handles
+            writer.WriteValueSafe(sceneManager.ObjectsMigratedIntoNewScene.Count);
+            foreach (var sceneHandleObjects in sceneManager.ObjectsMigratedIntoNewScene)
+            {
+                // Write the scene handle
+                writer.WriteValueSafe(sceneHandleObjects.Key);
+                // Write the number of NetworkObjectIds to expect
+                writer.WriteValueSafe(sceneHandleObjects.Value.Count);
+                foreach (var networkObject in sceneHandleObjects.Value)
+                {
+                    writer.WriteValueSafe(networkObject.NetworkObjectId);
+                }
+            }
+            // Once we are done, clear the table
+            sceneManager.ObjectsMigratedIntoNewScene.Clear();
+        }
+
+        /// <summary>
+        /// Deserialize scene handles and associated NetworkObjects that need to
+        /// be migrated into a new scene.
+        /// </summary>
+        private void DeserializeObjectsMovedIntoNewScene(FastBufferReader reader)
+        {
+            var sceneManager = m_NetworkManager.SceneManager;
+            var spawnManager = m_NetworkManager.SpawnManager;
+            // Just always assure this has no entries
+            sceneManager.ObjectsMigratedIntoNewScene.Clear();
+            var numberOfScenes = 0;
+            var sceneHandle = 0;
+            var objectCount = 0;
+            var networkObjectId = (ulong)0;
+            reader.ReadValueSafe(out numberOfScenes);
+            for (int i = 0; i < numberOfScenes; i++)
+            {
+                reader.ReadValueSafe(out sceneHandle);
+                sceneManager.ObjectsMigratedIntoNewScene.Add(sceneHandle, new List<NetworkObject>());
+                reader.ReadValueSafe(out objectCount);
+                for (int j = 0; j < objectCount; j++)
+                {
+                    reader.ReadValueSafe(out networkObjectId);
+                    if (!spawnManager.SpawnedObjects.ContainsKey(networkObjectId))
+                    {
+                        NetworkLog.LogError($"[Object Scene Migration] Trying to synchronize NetworkObjectId ({networkObjectId}) but it was not spawned or no longer exists!!");
+                        continue;
+                    }
+                    // Add NetworkObject scene migration to ObjectsMigratedIntoNewScene dictionary that is processed
+                    //
+                    sceneManager.ObjectsMigratedIntoNewScene[sceneHandle].Add(spawnManager.SpawnedObjects[networkObjectId]);
+                }
+            }
+        }
+
+
+        /// <summary>
+        /// While a client is synchronizing ObjectSceneChanged messages could be received.
+        /// This defers any ObjectSceneChanged message processing to occur after the client
+        /// has completed synchronization to assure the associated NetworkObjects being
+        /// migrated to a new scene are instantiated and spawned.
+        /// </summary>
+        private void DeferObjectsMovedIntoNewScene(FastBufferReader reader)
+        {
+            var sceneManager = m_NetworkManager.SceneManager;
+            var spawnManager = m_NetworkManager.SpawnManager;
+            var numberOfScenes = 0;
+            var sceneHandle = 0;
+            var objectCount = 0;
+            var networkObjectId = (ulong)0;
+
+            var deferredObjectsMovedEvent = new NetworkSceneManager.DeferredObjectsMovedEvent()
+            {
+                ObjectsMigratedTable = new Dictionary<int, List<ulong>>()
+            };
+
+            reader.ReadValueSafe(out numberOfScenes);
+            for (int i = 0; i < numberOfScenes; i++)
+            {
+                reader.ReadValueSafe(out sceneHandle);
+                deferredObjectsMovedEvent.ObjectsMigratedTable.Add(sceneHandle, new List<ulong>());
+                reader.ReadValueSafe(out objectCount);
+                for (int j = 0; j < objectCount; j++)
+                {
+                    reader.ReadValueSafe(out networkObjectId);
+                    deferredObjectsMovedEvent.ObjectsMigratedTable[sceneHandle].Add(networkObjectId);
+                }
+            }
+            sceneManager.DeferredObjectsMovedEvents.Add(deferredObjectsMovedEvent);
+        }
+
+        internal void ProcessDeferredObjectSceneChangedEvents()
+        {
+            var sceneManager = m_NetworkManager.SceneManager;
+            var spawnManager = m_NetworkManager.SpawnManager;
+            if (sceneManager.DeferredObjectsMovedEvents.Count == 0)
+            {
+                return;
+            }
+            foreach (var objectsMovedEvent in sceneManager.DeferredObjectsMovedEvents)
+            {
+                foreach (var keyEntry in objectsMovedEvent.ObjectsMigratedTable)
+                {
+                    if (!sceneManager.ObjectsMigratedIntoNewScene.ContainsKey(keyEntry.Key))
+                    {
+                        sceneManager.ObjectsMigratedIntoNewScene.Add(keyEntry.Key, new List<NetworkObject>());
+                    }
+                    foreach (var objectId in keyEntry.Value)
+                    {
+                        if (!spawnManager.SpawnedObjects.ContainsKey(objectId))
+                        {
+                            NetworkLog.LogWarning($"[Deferred][Object Scene Migration] Trying to synchronize NetworkObjectId ({objectId}) but it was not spawned or no longer exists!");
+                            continue;
+                        }
+                        var networkObject = spawnManager.SpawnedObjects[objectId];
+                        if (!sceneManager.ObjectsMigratedIntoNewScene[keyEntry.Key].Contains(networkObject))
+                        {
+                            sceneManager.ObjectsMigratedIntoNewScene[keyEntry.Key].Add(networkObject);
+                        }
+                    }
+                }
+                objectsMovedEvent.ObjectsMigratedTable.Clear();
+            }
+
+            sceneManager.DeferredObjectsMovedEvents.Clear();
+
+            // If there are any pending objects to migrate, then migrate them
+            if (sceneManager.ObjectsMigratedIntoNewScene.Count > 0)
+            {
+                sceneManager.MigrateNetworkObjectsIntoScenes();
+            }
+        }
+
         /// <summary>
         /// Used to release the pooled network buffer
         /// </summary>

Runtime/SceneManagement/SceneEventProgress.cs

@@ -58,12 +58,13 @@ namespace Unity.Netcode
         /// <summary>
         /// List of clientIds of those clients that is done loading the scene.
         /// </summary>
-        internal List<ulong> DoneClients { get; } = new List<ulong>();
+        internal Dictionary<ulong, bool> ClientsProcessingSceneEvent { get; } = new Dictionary<ulong, bool>();
+        internal List<ulong> ClientsThatDisconnected = new List<ulong>();
 
         /// <summary>
-        /// The local time when the scene event was "roughly started"
+        /// This is when the current scene event will have timed out
         /// </summary>
-        internal float TimeAtInitiation { get; }
+        internal float WhenSceneEventHasTimedOut;
 
         /// <summary>
         /// Delegate type for when the switch scene progress is completed. Either by all clients done loading the scene or by time out.
@@ -75,17 +76,15 @@ namespace Unity.Netcode
         /// </summary>
         internal OnCompletedDelegate OnComplete;
 
-        /// <summary>
+        internal Action<uint> OnSceneEventCompleted;
-        /// Is this scene switch progresses completed, all clients are done loading the scene or a timeout has occurred.
-        /// </summary>
-        internal bool IsCompleted { get; private set; }
-
-        internal bool TimedOut { get; private set; }
 
         /// <summary>
-        /// If all clients are done loading the scene, at the moment of completed.
+        /// This will make sure that we only have timed out if we never completed
         /// </summary>
-        internal bool AreAllClientsDoneLoading { get; private set; }
+        internal bool HasTimedOut()
+        {
+            return WhenSceneEventHasTimedOut <= m_NetworkManager.RealTimeProvider.RealTimeSinceStartup;
+        }
 
         /// <summary>
         /// The hash value generated from the full scene path
@@ -93,9 +92,10 @@ namespace Unity.Netcode
         internal uint SceneHash { get; set; }
 
         internal Guid Guid { get; } = Guid.NewGuid();
+        internal uint SceneEventId;
 
         private Coroutine m_TimeOutCoroutine;
-        private AsyncOperation m_SceneLoadOperation;
+        private AsyncOperation m_AsyncOperation;
 
         private NetworkManager m_NetworkManager { get; }
 
@@ -105,21 +105,85 @@ namespace Unity.Netcode
 
         internal LoadSceneMode LoadSceneMode;
 
-        internal List<ulong> ClientsThatStartedSceneEvent;
+        internal List<ulong> GetClientsWithStatus(bool completedSceneEvent)
+        {
+            var clients = new List<ulong>();
+            if (completedSceneEvent)
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that completed if the AsyncOperation is done.
+                if (m_NetworkManager.IsHost && m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
+
+                // Add all clients that completed the scene event
+                foreach (var clientStatus in ClientsProcessingSceneEvent)
+                {
+                    if (clientStatus.Value == completedSceneEvent)
+                    {
+                        clients.Add(clientStatus.Key);
+                    }
+                }
+            }
+            else
+            {
+                // If we are the host, then add the host-client to the list
+                // of clients that did not complete if the AsyncOperation is
+                // not done.
+                if (m_NetworkManager.IsHost && !m_AsyncOperation.isDone)
+                {
+                    clients.Add(m_NetworkManager.LocalClientId);
+                }
+
+                // If we are getting the list of clients that have not completed the
+                // scene event, then add any clients that disconnected during this
+                // scene event.
+                clients.AddRange(ClientsThatDisconnected);
+            }
+            return clients;
+        }
 
         internal SceneEventProgress(NetworkManager networkManager, SceneEventProgressStatus status = SceneEventProgressStatus.Started)
         {
             if (status == SceneEventProgressStatus.Started)
             {
-                // Track the clients that were connected when we started this event
-                ClientsThatStartedSceneEvent = new List<ulong>(networkManager.ConnectedClientsIds);
                 m_NetworkManager = networkManager;
+
+                if (networkManager.IsServer)
+                {
+                    m_NetworkManager.OnClientDisconnectCallback += OnClientDisconnectCallback;
+                    // Track the clients that were connected when we started this event
+                    foreach (var connectedClientId in networkManager.ConnectedClientsIds)
+                    {
+                        // Ignore the host client
+                        if (NetworkManager.ServerClientId == connectedClientId)
+                        {
+                            continue;
+                        }
+                        ClientsProcessingSceneEvent.Add(connectedClientId, false);
+                    }
+
+                    WhenSceneEventHasTimedOut = networkManager.RealTimeProvider.RealTimeSinceStartup + networkManager.NetworkConfig.LoadSceneTimeOut;
                     m_TimeOutCoroutine = m_NetworkManager.StartCoroutine(TimeOutSceneEventProgress());
-                TimeAtInitiation = Time.realtimeSinceStartup;
+                }
             }
             Status = status;
         }
 
+        /// <summary>
+        /// Remove the client from the clients processing the current scene event
+        /// Add this client to the clients that disconnected list
+        /// </summary>
+        private void OnClientDisconnectCallback(ulong clientId)
+        {
+            if (ClientsProcessingSceneEvent.ContainsKey(clientId))
+            {
+                ClientsThatDisconnected.Add(clientId);
+                ClientsProcessingSceneEvent.Remove(clientId);
+            }
+        }
+
         /// <summary>
         /// Coroutine that checks to see if the scene event is complete every network tick period.
         /// This will handle completing the scene event when one or more client(s) disconnect(s)
@@ -129,79 +193,107 @@ namespace Unity.Netcode
         internal IEnumerator TimeOutSceneEventProgress()
         {
             var waitForNetworkTick = new WaitForSeconds(1.0f / m_NetworkManager.NetworkConfig.TickRate);
-            while (!TimedOut && !IsCompleted)
+            while (!HasTimedOut())
             {
                 yield return waitForNetworkTick;
 
-                CheckCompletion();
+                TryFinishingSceneEventProgress();
-                if (!IsCompleted)
-                {
-                    TimedOut = TimeAtInitiation - Time.realtimeSinceStartup >= m_NetworkManager.NetworkConfig.LoadSceneTimeOut;
             }
         }
-        }
-
-        internal void AddClientAsDone(ulong clientId)
-        {
-            DoneClients.Add(clientId);
-            CheckCompletion();
-        }
-
-        internal void RemoveClientAsDone(ulong clientId)
-        {
-            DoneClients.Remove(clientId);
-            CheckCompletion();
-        }
-
-        internal void SetSceneLoadOperation(AsyncOperation sceneLoadOperation)
-        {
-            m_SceneLoadOperation = sceneLoadOperation;
-            m_SceneLoadOperation.completed += operation => CheckCompletion();
-        }
 
         /// <summary>
-        /// Called only on the server-side during integration test (NetcodeIntegrationTest specific)
+        /// Sets the client's scene event progress to finished/true
-        /// scene loading and unloading.
-        ///
-        /// Note: During integration testing we must queue all scene loading and unloading requests for
-        /// both the server and all clients so they can be processed in a FIFO/linear fashion to avoid
-        /// conflicts when the  <see cref="SceneManager.sceneLoaded"/> and <see cref="SceneManager.sceneUnloaded"/>
-        /// events are triggered. The Completed action simulates the <see cref="AsyncOperation.completed"/> event.
-        /// (See: Unity.Netcode.TestHelpers.Runtime.IntegrationTestSceneHandler)
         /// </summary>
-        internal void SetSceneLoadOperation(ISceneManagerHandler.SceneEventAction sceneEventAction)
+        internal void ClientFinishedSceneEvent(ulong clientId)
         {
-            sceneEventAction.Completed = SetComplete;
+            if (ClientsProcessingSceneEvent.ContainsKey(clientId))
+            {
+                ClientsProcessingSceneEvent[clientId] = true;
+                TryFinishingSceneEventProgress();
+            }
         }
 
         /// <summary>
-        /// Finalizes the SceneEventProgress
+        /// Determines if the scene event has finished for both
+        /// client(s) and server.
         /// </summary>
-        internal void SetComplete()
+        /// <remarks>
+        /// The server checks if all known clients processing this scene event
+        /// have finished and then it returns its local AsyncOperation status.
+        /// Clients finish when their AsyncOperation finishes.
+        /// </remarks>
+        private bool HasFinished()
         {
-            IsCompleted = true;
+            // If the network session is terminated/terminating then finish tracking
-            AreAllClientsDoneLoading = true;
+            // this scene event
+            if (!IsNetworkSessionActive())
+            {
+                return true;
+            }
 
-            // If OnComplete is not registered or it is and returns true then remove this from the progress tracking
+            // Clients skip over this
-            if (OnComplete == null || (OnComplete != null && OnComplete.Invoke(this)))
+            foreach (var clientStatus in ClientsProcessingSceneEvent)
             {
+                if (!clientStatus.Value)
+                {
+                    return false;
+                }
+            }
+
+            // Return the local scene event's AsyncOperation status
+            // Note: Integration tests process scene loading through a queue
+            // and the AsyncOperation could not be assigned for several
+            // network tick periods. Return false if that is the case.
+            return m_AsyncOperation == null ? false : m_AsyncOperation.isDone;
+        }
+
+        /// <summary>
+        /// Sets the AsyncOperation for the scene load/unload event
+        /// </summary>
+        internal void SetAsyncOperation(AsyncOperation asyncOperation)
+        {
+            m_AsyncOperation = asyncOperation;
+            m_AsyncOperation.completed += new Action<AsyncOperation>(asyncOp2 =>
+            {
+                // Don't invoke the callback if the network session is disconnected
+                // during a SceneEventProgress
+                if (IsNetworkSessionActive())
+                {
+                    OnSceneEventCompleted?.Invoke(SceneEventId);
+                }
+
+                // Go ahead and try finishing even if the network session is terminated/terminating
+                // as we might need to stop the coroutine
+                TryFinishingSceneEventProgress();
+            });
+        }
+
+
+        internal bool IsNetworkSessionActive()
+        {
+            return m_NetworkManager != null && m_NetworkManager.IsListening && !m_NetworkManager.ShutdownInProgress;
+        }
+
+        /// <summary>
+        /// Will try to finish the current scene event in progress as long as
+        /// all conditions are met.
+        /// </summary>
+        internal void TryFinishingSceneEventProgress()
+        {
+            if (HasFinished() || HasTimedOut())
+            {
+                // Don't attempt to finalize this scene event if we are no longer listening or a shutdown is in progress
+                if (IsNetworkSessionActive())
+                {
+                    OnComplete?.Invoke(this);
                     m_NetworkManager.SceneManager.SceneEventProgressTracking.Remove(Guid);
+                    m_NetworkManager.OnClientDisconnectCallback -= OnClientDisconnectCallback;
                 }
+
+                if (m_TimeOutCoroutine != null)
+                {
                     m_NetworkManager.StopCoroutine(m_TimeOutCoroutine);
                 }
-
-        internal void CheckCompletion()
-        {
-            try
-            {
-                if ((!IsCompleted && DoneClients.Count == m_NetworkManager.ConnectedClientsList.Count && (m_SceneLoadOperation == null || m_SceneLoadOperation.isDone)) || (!IsCompleted && TimedOut))
-                {
-                    SetComplete();
-                }
-            }
-            catch (Exception ex)
-            {
-                Debug.LogException(ex);
             }
         }
     }

Runtime/Serialization/BitReader.cs

@@ -21,6 +21,8 @@ namespace Unity.Netcode
 
         private const int k_BitsPerByte = 8;
 
+        private int BytePosition => m_BitPosition >> 3;
+
         /// <summary>
         /// Whether or not the current BitPosition is evenly divisible by 8. I.e. whether or not the BitPosition is at a byte boundary.
         /// </summary>
@@ -98,11 +100,6 @@ namespace Unity.Netcode
                 throw new ArgumentOutOfRangeException(nameof(bitCount), "Cannot read more than 64 bits from a 64-bit value!");
             }
 
-            if (bitCount < 0)
-            {
-                throw new ArgumentOutOfRangeException(nameof(bitCount), "Cannot read fewer than 0 bits!");
-            }
-
             int checkPos = (int)(m_BitPosition + bitCount);
             if (checkPos > m_AllowedBitwiseReadMark)
             {
@@ -165,7 +162,7 @@ namespace Unity.Netcode
 #endif
 
             int offset = m_BitPosition & 7;
-            int pos = m_BitPosition >> 3;
+            int pos = BytePosition;
             bit = (m_BufferPointer[pos] & (1 << offset)) != 0;
             ++m_BitPosition;
         }
@@ -175,7 +172,7 @@ namespace Unity.Netcode
         {
             var val = new T();
             byte* ptr = ((byte*)&val) + offsetBytes;
-            byte* bufferPointer = m_BufferPointer + m_Position;
+            byte* bufferPointer = m_BufferPointer + BytePosition;
             UnsafeUtility.MemCpy(ptr, bufferPointer, bytesToRead);
 
             m_BitPosition += bytesToRead * k_BitsPerByte;

Runtime/Serialization/BitWriter.cs

@@ -29,6 +29,8 @@ namespace Unity.Netcode
             get => (m_BitPosition & 7) == 0;
         }
 
+        private int BytePosition => m_BitPosition >> 3;
+
         internal unsafe BitWriter(FastBufferWriter writer)
         {
             m_Writer = writer;
@@ -181,7 +183,7 @@ namespace Unity.Netcode
 #endif
 
             int offset = m_BitPosition & 7;
-            int pos = m_BitPosition >> 3;
+            int pos = BytePosition;
             ++m_BitPosition;
             m_BufferPointer[pos] = (byte)(bit ? (m_BufferPointer[pos] & ~(1 << offset)) | (1 << offset) : (m_BufferPointer[pos] & ~(1 << offset)));
         }
@@ -190,7 +192,7 @@ namespace Unity.Netcode
         private unsafe void WritePartialValue<T>(T value, int bytesToWrite, int offsetBytes = 0) where T : unmanaged
         {
             byte* ptr = ((byte*)&value) + offsetBytes;
-            byte* bufferPointer = m_BufferPointer + m_Position;
+            byte* bufferPointer = m_BufferPointer + BytePosition;
             UnsafeUtility.MemCpy(bufferPointer, ptr, bytesToWrite);
 
             m_BitPosition += bytesToWrite * k_BitsPerByte;

Runtime/Serialization/BufferSerializer.cs

@@ -7,14 +7,10 @@ namespace Unity.Netcode
     /// <summary>
     /// Two-way serializer wrapping FastBufferReader or FastBufferWriter.
     ///
-    /// Implemented as a ref struct for two reasons:
+    /// Implemented as a ref struct to help enforce the requirement that
-    /// 1. The BufferSerializer cannot outlive the FBR/FBW it wraps or using it will cause a crash
+    /// the BufferSerializer cannot outlive the FBR/FBW it wraps or using it will cause a crash
-    /// 2. The BufferSerializer must always be passed by reference and can't be copied
     ///
-    /// Ref structs help enforce both of those rules: they can't ref live the stack context in which they were
+    /// BufferSerializer doesn't wrap FastBufferReader or FastBufferWriter directly because it can't.
-    /// created, and they're always passed by reference no matter what.
-    ///
-    /// BufferSerializer doesn't wrapp FastBufferReader or FastBufferWriter directly because it can't.
     /// ref structs can't implement interfaces, and in order to be able to have two different implementations with
     /// the same interface (which allows us to avoid an "if(IsReader)" on every call), the thing directly wrapping
     /// the struct has to implement an interface. So IReaderWriter exists as the interface,

Runtime/Serialization/BufferSerializerReader.cs

@@ -34,7 +34,7 @@ namespace Unity.Netcode
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForEnums unused = default) where T : unmanaged, Enum => m_Reader.ReadValueSafe(out value);
         public void SerializeValue<T>(ref T value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValueSafe(out value);
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForStructs unused = default) where T : unmanaged, INetworkSerializeByMemcpy => m_Reader.ReadValueSafe(out value);
-        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadValue(out value);
+        public void SerializeValue<T>(ref T value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadNetworkSerializableInPlace(ref value);
         public void SerializeValue<T>(ref T[] value, FastBufferWriter.ForNetworkSerializable unused = default) where T : INetworkSerializable, new() => m_Reader.ReadValue(out value);
 
         public void SerializeValue<T>(ref T value, FastBufferWriter.ForFixedStrings unused = default)

Runtime/Serialization/BytePacker.cs

@@ -50,7 +50,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteValuePacked(FastBufferWriter writer, float value)
         {
-            WriteUInt32Packed(writer, ToUint(value));
+            WriteValueBitPacked(writer, ToUint(value));
         }
 
         /// <summary>
@@ -61,7 +61,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void WriteValuePacked(FastBufferWriter writer, double value)
         {
-            WriteUInt64Packed(writer, ToUlong(value));
+            WriteValueBitPacked(writer, ToUlong(value));
         }
 
         /// <summary>
@@ -98,7 +98,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, short value) => WriteUInt32Packed(writer, (ushort)Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, short value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned short (UInt16) as a varint to the buffer.
@@ -109,7 +109,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, ushort value) => WriteUInt32Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, ushort value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write a two-byte character as a varint to the buffer.
@@ -120,7 +120,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="c">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, char c) => WriteUInt32Packed(writer, c);
+        public static void WriteValuePacked(FastBufferWriter writer, char c) => WriteValueBitPacked(writer, c);
 
         /// <summary>
         /// Write a signed int (Int32) as a ZigZag encoded varint to the buffer.
@@ -128,7 +128,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, int value) => WriteUInt32Packed(writer, (uint)Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned int (UInt32) to the buffer.
@@ -136,7 +136,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, uint value) => WriteUInt32Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, uint value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write an unsigned long (UInt64) to the buffer.
@@ -144,7 +144,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, ulong value) => WriteUInt64Packed(writer, value);
+        public static void WriteValuePacked(FastBufferWriter writer, ulong value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Write a signed long (Int64) as a ZigZag encoded varint to the buffer.
@@ -152,7 +152,7 @@ namespace Unity.Netcode
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">Value to write</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void WriteValuePacked(FastBufferWriter writer, long value) => WriteUInt64Packed(writer, Arithmetic.ZigZagEncode(value));
+        public static void WriteValuePacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, value);
 
         /// <summary>
         /// Convenience method that writes two packed Vector3 from the ray to the buffer
@@ -282,231 +282,183 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public void WriteValueBitPacked<T>(FastBufferWriter writer, T value) where T: unmanaged => writer.WriteValueSafe(value);
 #else
-
         /// <summary>
-        /// Maximum serializable value for a BitPacked ushort (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const ushort BitPackedUshortMax = (1 << 15) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked short
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const short BitPackedShortMax = (1 << 14) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked ushort
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const short BitPackedShortMin = -(1 << 14);
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked uint (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const uint BitPackedUintMax = (1 << 30) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked int
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const int BitPackedIntMax = (1 << 29) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked int
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const int BitPackedIntMin = -(1 << 29);
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked ulong (minimum for unsigned is 0)
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const ulong BitPackedULongMax = (1L << 61) - 1;
 
         /// <summary>
-        /// Maximum serializable value for a BitPacked long
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const long BitPackedLongMax = (1L << 60) - 1;
 
         /// <summary>
-        /// Minimum serializable value size for a BitPacked long
+        /// Obsolete value that no longer carries meaning. Do not use.
         /// </summary>
         public const long BitPackedLongMin = -(1L << 60);
 
         /// <summary>
-        /// Writes a 14-bit signed short to the buffer in a bit-encoded packed format.
+        /// Writes a 16-bit signed short to the buffer in a bit-encoded packed format.
-        /// The first bit indicates whether the value is 1 byte or 2.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
-        /// The sign bit takes up another bit.
+        /// are still able to be compressed.
-        /// That leaves 14 bits for the value.
+        /// The first two bits indicate whether the value is 1, 2, or 3 bytes.
-        /// A value greater than 2^14-1 or less than -2^14 will throw an exception in editor and development builds.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its two
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
-        /// most significant bits after zig-zag encoding.
+        /// by the original unmodified 16-bit value in the next 2 bytes.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
         public static void WriteValueBitPacked(FastBufferWriter writer, short value) => WriteValueBitPacked(writer, (ushort)Arithmetic.ZigZagEncode(value));
 
         /// <summary>
-        /// Writes a 15-bit unsigned short to the buffer in a bit-encoded packed format.
+        /// Writes a 16-bit unsigned short to the buffer in a bit-encoded packed format.
-        /// The first bit indicates whether the value is 1 byte or 2.
+        /// The first two bits indicate whether the value is 1, 2, or 3 bytes.
-        /// That leaves 15 bits for the value.
+        /// If the value uses 14 bits or less, the remaining 14 bits contain the value.
-        /// A value greater than 2^15-1 will throw an exception in editor and development builds.
+        /// For performance, reasons, if the value is 15 bits or more, there will be six 0 bits, followed
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its
+        /// by the original unmodified 16-bit value in the next 2 bytes.
-        /// most significant bit.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
         public static void WriteValueBitPacked(FastBufferWriter writer, ushort value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            if (value > (1 << 14) - 1)
-            if (value >= BitPackedUshortMax)
             {
-                throw new ArgumentException("BitPacked ushorts must be <= 15 bits");
+                if (!writer.TryBeginWriteInternal(3))
-            }
-#endif
-
-            if (value <= 0b0111_1111)
-            {
-                if (!writer.TryBeginWriteInternal(1))
                 {
                     throw new OverflowException("Writing past the end of the buffer");
                 }
-                writer.WriteByte((byte)(value << 1));
+                writer.WriteByte(3);
+                writer.WriteValue(value);
                 return;
             }
 
-            if (!writer.TryBeginWriteInternal(2))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteValue((ushort)((value << 1) | 0b1));
-        }
-
-        /// <summary>
-        /// Writes a 29-bit signed int to the buffer in a bit-encoded packed format.
-        /// The first two bits indicate whether the value is 1, 2, 3, or 4 bytes.
-        /// The sign bit takes up another bit.
-        /// That leaves 29 bits for the value.
-        /// A value greater than 2^29-1 or less than -2^29 will throw an exception in editor and development builds.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its three
-        /// most significant bits after zig-zag encoding.
-        /// </summary>
-        /// <param name="writer">The writer to write to</param>
-        /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, (uint)Arithmetic.ZigZagEncode(value));
-
-        /// <summary>
-        /// Writes a 30-bit unsigned int to the buffer in a bit-encoded packed format.
-        /// The first two bits indicate whether the value is 1, 2, 3, or 4 bytes.
-        /// That leaves 30 bits for the value.
-        /// A value greater than 2^30-1 will throw an exception in editor and development builds.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its two
-        /// most significant bits.
-        /// </summary>
-        /// <param name="writer">The writer to write to</param>
-        /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
-        {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
-            if (value > BitPackedUintMax)
-            {
-                throw new ArgumentException("BitPacked uints must be <= 30 bits");
-            }
-#endif
             value <<= 2;
             var numBytes = BitCounter.GetUsedByteCount(value);
             if (!writer.TryBeginWriteInternal(numBytes))
             {
                 throw new OverflowException("Writing past the end of the buffer");
             }
-            writer.WritePartialValue(value | (uint)(numBytes - 1), numBytes);
+            writer.WritePartialValue(value | (ushort)(numBytes), numBytes);
         }
 
         /// <summary>
-        /// Writes a 60-bit signed long to the buffer in a bit-encoded packed format.
+        /// Writes a 32-bit signed int to the buffer in a bit-encoded packed format.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
-        /// The sign bit takes up another bit.
+        /// are still able to be compressed.
-        /// That leaves 60 bits for the value.
+        /// The first three bits indicate whether the value is 1, 2, 3, 4, or 5 bytes.
-        /// A value greater than 2^60-1 or less than -2^60 will throw an exception in editor and development builds.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its four
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
-        /// most significant bits after zig-zag encoding.
+        /// by the original unmodified 32-bit value in the next 4 bytes.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, Arithmetic.ZigZagEncode(value));
+        public static void WriteValueBitPacked(FastBufferWriter writer, int value) => WriteValueBitPacked(writer, (uint)Arithmetic.ZigZagEncode(value));
 
         /// <summary>
-        /// Writes a 61-bit unsigned long to the buffer in a bit-encoded packed format.
+        /// Writes a 32-bit unsigned int to the buffer in a bit-encoded packed format.
-        /// The first three bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, or 8 bytes.
+        /// The first three bits indicate whether the value is 1, 2, 3, 4, or 5 bytes.
-        /// That leaves 31 bits for the value.
+        /// If the value uses 29 bits or less, the remaining 29 bits contain the value.
-        /// A value greater than 2^61-1 will throw an exception in editor and development builds.
+        /// For performance, reasons, if the value is 30 bits or more, there will be five 0 bits, followed
-        /// In release builds builds the exception is not thrown and the value is truncated by losing its three
+        /// by the original unmodified 32-bit value in the next 4 bytes.
-        /// most significant bits.
         /// </summary>
         /// <param name="writer">The writer to write to</param>
         /// <param name="value">The value to pack</param>
-        public static void WriteValueBitPacked(FastBufferWriter writer, ulong value)
+        public static void WriteValueBitPacked(FastBufferWriter writer, uint value)
         {
-#if DEVELOPMENT_BUILD || UNITY_EDITOR
+            if (value > (1 << 29) - 1)
-            if (value > BitPackedULongMax)
             {
-                throw new ArgumentException("BitPacked ulongs must be <= 61 bits");
+                if (!writer.TryBeginWriteInternal(5))
+                {
+                    throw new OverflowException("Writing past the end of the buffer");
                 }
-#endif
+                writer.WriteByte(5);
+                writer.WriteValue(value);
+                return;
+            }
+
             value <<= 3;
             var numBytes = BitCounter.GetUsedByteCount(value);
             if (!writer.TryBeginWriteInternal(numBytes))
             {
                 throw new OverflowException("Writing past the end of the buffer");
             }
-            writer.WritePartialValue(value | (uint)(numBytes - 1), numBytes);
+            writer.WritePartialValue(value | (uint)(numBytes), numBytes);
+        }
+
+        /// <summary>
+        /// Writes a 64-bit signed long to the buffer in a bit-encoded packed format.
+        /// Zig-zag encoding is used to move the sign bit to the least significant bit, so that negative values
+        /// are still able to be compressed.
+        /// The first four bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, 8, or 9 bytes.
+        /// If the value uses 60 bits or less, the remaining 60 bits contain the value.
+        /// For performance, reasons, if the value is 61 bits or more, there will be four 0 bits, followed
+        /// by the original unmodified 64-bit value in the next 8 bytes.
+        /// </summary>
+        /// <param name="writer">The writer to write to</param>
+        /// <param name="value">The value to pack</param>
+        public static void WriteValueBitPacked(FastBufferWriter writer, long value) => WriteValueBitPacked(writer, Arithmetic.ZigZagEncode(value));
+
+        /// <summary>
+        /// Writes a 64-bit unsigned long to the buffer in a bit-encoded packed format.
+        /// The first four bits indicate whether the value is 1, 2, 3, 4, 5, 6, 7, 8, or 9 bytes.
+        /// If the value uses 60 bits or less, the remaining 60 bits contain the value.
+        /// For performance, reasons, if the value is 61 bits or more, there will be four 0 bits, followed
+        /// by the original unmodified 64-bit value in the next 8 bytes.
+        /// </summary>
+        /// <param name="writer">The writer to write to</param>
+        /// <param name="value">The value to pack</param>
+        public static void WriteValueBitPacked(FastBufferWriter writer, ulong value)
+        {
+            if (value > (1L << 60) - 1)
+            {
+                if (!writer.TryBeginWriteInternal(9))
+                {
+                    throw new OverflowException("Writing past the end of the buffer");
+                }
+                writer.WriteByte(9);
+                writer.WriteValue(value);
+                return;
+            }
+
+            value <<= 4;
+            var numBytes = BitCounter.GetUsedByteCount(value);
+            if (!writer.TryBeginWriteInternal(numBytes))
+            {
+                throw new OverflowException("Writing past the end of the buffer");
+            }
+            writer.WritePartialValue(value | (uint)(numBytes), numBytes);
         }
 #endif
-
-        private static void WriteUInt64Packed(FastBufferWriter writer, ulong value)
-        {
-            if (value <= 240)
-            {
-                writer.WriteByteSafe((byte)value);
-                return;
-            }
-            if (value <= 2287)
-            {
-                writer.WriteByteSafe((byte)(((value - 240) >> 8) + 241));
-                writer.WriteByteSafe((byte)(value - 240));
-                return;
-            }
-            var writeBytes = BitCounter.GetUsedByteCount(value);
-
-            if (!writer.TryBeginWriteInternal(writeBytes + 1))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteByte((byte)(247 + writeBytes));
-            writer.WritePartialValue(value, writeBytes);
-        }
-
-        // Looks like the same code as WriteUInt64Packed?
-        // It's actually different because it will call the more efficient 32-bit version
-        // of BytewiseUtility.GetUsedByteCount().
-        private static void WriteUInt32Packed(FastBufferWriter writer, uint value)
-        {
-            if (value <= 240)
-            {
-                writer.WriteByteSafe((byte)value);
-                return;
-            }
-            if (value <= 2287)
-            {
-                writer.WriteByteSafe((byte)(((value - 240) >> 8) + 241));
-                writer.WriteByteSafe((byte)(value - 240));
-                return;
-            }
-            var writeBytes = BitCounter.GetUsedByteCount(value);
-
-            if (!writer.TryBeginWriteInternal(writeBytes + 1))
-            {
-                throw new OverflowException("Writing past the end of the buffer");
-            }
-            writer.WriteByte((byte)(247 + writeBytes));
-            writer.WritePartialValue(value, writeBytes);
-        }
-
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe uint ToUint<T>(T value) where T : unmanaged
         {

Runtime/Serialization/ByteUnpacker.cs

@@ -11,7 +11,6 @@ namespace Unity.Netcode
     /// </summary>
     public static class ByteUnpacker
     {
-
 #if UNITY_NETCODE_DEBUG_NO_PACKING
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -58,7 +57,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out float value)
         {
-            ReadUInt32Packed(reader, out uint asUInt);
+            ReadValueBitPacked(reader, out uint asUInt);
             value = ToSingle(asUInt);
         }
 
@@ -70,7 +69,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out double value)
         {
-            ReadUInt64Packed(reader, out ulong asULong);
+            ReadValueBitPacked(reader, out ulong asULong);
             value = ToDouble(asULong);
         }
 
@@ -109,11 +108,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out short value)
+        public static void ReadValuePacked(FastBufferReader reader, out short value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (short)Arithmetic.ZigZagDecode(readValue);
-        }
 
         /// <summary>
         /// Read an unsigned short (UInt16) as a varint from the stream.
@@ -121,11 +116,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out ushort value)
+        public static void ReadValuePacked(FastBufferReader reader, out ushort value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (ushort)readValue;
-        }
 
         /// <summary>
         /// Read a two-byte character as a varint from the stream.
@@ -135,7 +126,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out char c)
         {
-            ReadUInt32Packed(reader, out uint readValue);
+            ReadValueBitPacked(reader, out ushort readValue);
             c = (char)readValue;
         }
 
@@ -145,11 +136,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out int value)
+        public static void ReadValuePacked(FastBufferReader reader, out int value) => ReadValueBitPacked(reader, out value);
-        {
-            ReadUInt32Packed(reader, out uint readValue);
-            value = (int)Arithmetic.ZigZagDecode(readValue);
-        }
 
         /// <summary>
         /// Read an unsigned int (UInt32) from the stream.
@@ -157,7 +144,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out uint value) => ReadUInt32Packed(reader, out value);
+        public static void ReadValuePacked(FastBufferReader reader, out uint value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read an unsigned long (UInt64) from the stream.
@@ -165,7 +152,7 @@ namespace Unity.Netcode
         /// <param name="reader">The reader to read from</param>
         /// <param name="value">Value to read</param>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static void ReadValuePacked(FastBufferReader reader, out ulong value) => ReadUInt64Packed(reader, out value);
+        public static void ReadValuePacked(FastBufferReader reader, out ulong value) => ReadValueBitPacked(reader, out value);
 
         /// <summary>
         /// Read a signed long (Int64) as a ZigZag encoded varint from the stream.
@@ -175,8 +162,7 @@ namespace Unity.Netcode
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void ReadValuePacked(FastBufferReader reader, out long value)
         {
-            ReadUInt64Packed(reader, out ulong readValue);
+            ReadValueBitPacked(reader, out value);
-            value = Arithmetic.ZigZagDecode(readValue);
         }
 
         /// <summary>
@@ -341,7 +327,9 @@ namespace Unity.Netcode
             ushort returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b1) + 1;
+            // Mask out the first two bits - they contain the total byte count
+            // (1, 2, or 3)
+            int numBytes = (data[0] & 0b11);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -350,17 +338,23 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
+                case 3:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    value = returnValue;
+                    return;
                 default:
                     throw new InvalidOperationException("Could not read bit-packed value: impossible byte count");
             }
 
-            value = (ushort)(returnValue >> 1);
+            value = (ushort)(returnValue >> 2);
         }
 
         /// <summary>
@@ -386,7 +380,8 @@ namespace Unity.Netcode
             uint returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b11) + 1;
+            // Mask out the first three bits - they contain the total byte count (1-5)
+            int numBytes = (data[0] & 0b111);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -395,26 +390,34 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
                     break;
+                case 5:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    ptr[2] = data[3];
+                    ptr[3] = data[4];
+                    value = returnValue;
+                    return;
             }
 
-            value = returnValue >> 2;
+            value = returnValue >> 3;
         }
 
         /// <summary>
@@ -440,7 +443,8 @@ namespace Unity.Netcode
             ulong returnValue = 0;
             byte* ptr = ((byte*)&returnValue);
             byte* data = reader.GetUnsafePtrAtCurrentPosition();
-            int numBytes = (data[0] & 0b111) + 1;
+            // Mask out the first four bits - they contain the total byte count (1-9)
+            int numBytes = (data[0] & 0b1111);
             if (!reader.TryBeginReadInternal(numBytes))
             {
                 throw new OverflowException("Reading past the end of the buffer");
@@ -449,109 +453,74 @@ namespace Unity.Netcode
             switch (numBytes)
             {
                 case 1:
-                    *ptr = *data;
+                    ptr[0] = data[0];
                     break;
                 case 2:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
                     break;
                 case 3:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
                     break;
                 case 4:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
                     break;
                 case 5:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
                     break;
                 case 6:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
                     break;
                 case 7:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
-                    *(ptr + 6) = *(data + 6);
+                    ptr[6] = data[6];
                     break;
                 case 8:
-                    *ptr = *data;
+                    ptr[0] = data[0];
-                    *(ptr + 1) = *(data + 1);
+                    ptr[1] = data[1];
-                    *(ptr + 2) = *(data + 2);
+                    ptr[2] = data[2];
-                    *(ptr + 3) = *(data + 3);
+                    ptr[3] = data[3];
-                    *(ptr + 4) = *(data + 4);
+                    ptr[4] = data[4];
-                    *(ptr + 5) = *(data + 5);
+                    ptr[5] = data[5];
-                    *(ptr + 6) = *(data + 6);
+                    ptr[6] = data[6];
-                    *(ptr + 7) = *(data + 7);
+                    ptr[7] = data[7];
                     break;
+                case 9:
+                    // First byte contains no data, it's just a marker. The data is in the remaining two bytes.
+                    ptr[0] = data[1];
+                    ptr[1] = data[2];
+                    ptr[2] = data[3];
+                    ptr[3] = data[4];
+                    ptr[4] = data[5];
+                    ptr[5] = data[6];
+                    ptr[6] = data[7];
+                    ptr[7] = data[8];
+                    value = returnValue;
+                    return;
             }
 
-            value = returnValue >> 3;
+            value = returnValue >> 4;
         }
 #endif
-        private static void ReadUInt64Packed(FastBufferReader reader, out ulong value)
-        {
-            reader.ReadByteSafe(out byte firstByte);
-            if (firstByte <= 240)
-            {
-                value = firstByte;
-                return;
-            }
-
-            if (firstByte <= 248)
-            {
-                reader.ReadByteSafe(out byte secondByte);
-                value = 240UL + ((firstByte - 241UL) << 8) + secondByte;
-                return;
-            }
-
-            var numBytes = firstByte - 247;
-            if (!reader.TryBeginReadInternal(numBytes))
-            {
-                throw new OverflowException("Reading past the end of the buffer");
-            }
-            reader.ReadPartialValue(out value, numBytes);
-        }
-
-        private static void ReadUInt32Packed(FastBufferReader reader, out uint value)
-        {
-            reader.ReadByteSafe(out byte firstByte);
-            if (firstByte <= 240)
-            {
-                value = firstByte;
-                return;
-            }
-
-            if (firstByte <= 248)
-            {
-                reader.ReadByteSafe(out byte secondByte);
-                value = 240U + ((firstByte - 241U) << 8) + secondByte;
-                return;
-            }
-
-            var numBytes = firstByte - 247;
-            if (!reader.TryBeginReadInternal(numBytes))
-            {
-                throw new OverflowException("Reading past the end of the buffer");
-            }
-            reader.ReadPartialValue(out value, numBytes);
-        }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe float ToSingle<T>(T value) where T : unmanaged

Runtime/Serialization/ByteUtility.cs

@@ -0,0 +1,58 @@
+using System.Runtime.CompilerServices;
+
+namespace Unity.Netcode
+{
+    internal class ByteUtility
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static unsafe byte ToByte(bool b) => *(byte*)&b;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(byte bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref byte bitField, ushort bitPosition, bool value)
+        {
+            bitField = (byte)((bitField & ~(1 << bitPosition)) | (ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(ushort bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref ushort bitField, ushort bitPosition, bool value)
+        {
+            bitField = (ushort)((bitField & ~(1 << bitPosition)) | (ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(uint bitField, ushort bitPosition)
+        {
+            return (bitField & (1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref uint bitField, ushort bitPosition, bool value)
+        {
+            bitField = (uint)((bitField & ~(1 << bitPosition)) | ((uint)ToByte(value) << bitPosition));
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static bool GetBit(ulong bitField, ushort bitPosition)
+        {
+            return (bitField & (ulong)(1 << bitPosition)) != 0;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        internal static void SetBit(ref ulong bitField, ushort bitPosition, bool value)
+        {
+            bitField = ((bitField & (ulong)~(1 << bitPosition)) | ((ulong)ToByte(value) << bitPosition));
+        }
+    }
+}

Runtime/Serialization/ByteUtility.cs.meta

@@ -0,0 +1,3 @@
+fileFormatVersion: 2
+guid: 25bb0dd7157c423b8cfe0ecf06e15ae5
+timeCreated: 1666711082