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UdonSharp 0.x (the .unitypackage version) is deprecated and no longer supported. This new version is easy to get through the Creator Companion, which will help you keep it up-to-date as well. We recommend you Migrate your Projects using the Creator Companion. If you want to do the migration manually, read Manual Migration.

New Features in UdonSharp 1.0

  • More C# features in your UdonSharp programs:
    • static methods
    • Generic static methods
    • params, out, ref, and default parameters
    • Extension methods
    • Inheritance, virtual methods, and abstract classes
    • Partial classes
    • Enums
  • Multi-edit multiple UdonSharp scripts in the Unity inspector
  • Prefab variants, instances, and nesting are now fully supported
  • Editor scripting has been overhauled and simplified
  • Compiler fixes and optimizations
  • Fixed various bugs, edge cases, and other rough edges

Known Issues

Nested Prefabs

Issue: UdonSharp always warned against using nested prefabs, and now they will completely break in some circumstances.

Symptoms: Errors like Cannot upgrade scene behaviour 'SomethingOrOther' since its prefab must be upgraded

How to Fix: Unpack the prefab in your 0.x UdonSharp project first. You can also open the "Udon Sharp" menu item and choose "Force Upgrade".

Does Not Belong to U# Assembly

Issue: Libraries with their own Assembly Definitions need to have an U# assembly definition, too.

Symptoms: An error like this: [UdonSharp] Script 'Assets/MyScript.cs' does not belong to a U# assembly, have you made a U# assembly definition for the assembly the script is a part of?

How to Fix:

  1. Use the Project window to find the file ending in .asmdef in the same or a parent directory of the script in question.
  2. Right-click in the folder which has this Assembly Definition and choose Create > U# Assembly Definition.
  3. Select this new U# asmdef, and use the inspector to set its "Source Assembly" to the other Assembly Definition File.
  4. You may need to restart Unity after doing this.


Issue: Some packages include their own copy of this JSON library, which the VRCSDK pulls in itself. This results in two copies of the library.

Symptoms: Errors in your console which mention the above library. It might not be at the front of the sentence, but something like System.TypeInitializationException: the type initializer for blah blah blah...Assets/SketchfabForUnity/Dependencies/Libraries/Newtonsoft.Json.dll

How to Fix: Remove any copies of Newtonsoft.Json.dll from your Assets folder. The VRCSDK will provide it for any package that needs it through the Package Manager.

Other breaking changes

  • Your U# behaviour name must match the .cs file name
  • Duplicate program assets may not reference the same .cs file
  • Program assets must point to a script and may not be empty
  • Editor scripting is now different: Data is owned by a C# proxy of the UdonSharpBehaviour, and the corresponding UdonBehaviour is empty until runtime.
  • Obsoleted overloads for station and player join events may no longer be used

Manual Migration

Follow these steps to upgrade a project that uses a version of UdonSharp below 1.0 without using the Creator Companion:

  1. Back up your project.
  2. Delete the VRCSDK folder, Udon folder, UdonSharp folder, and Gizmos/UdonSharp folders from your project's "Assets" folder.
  3. Download and install the Unity Package versions of the World SDK.
  4. Download and install the Unity Package version of the UdonSharp SDK.