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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.

Migrating Projects using the Creator Companion.

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