How to Upgrade Your .NET WebAssembly Application to .NET 10

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Introduction

Upgrading your .NET WebAssembly (WASM) application from .NET 8 to .NET 10 unlocks significant performance gains and simplifies your deployment pipeline. Microsoft’s Copilot Studio recently completed this migration, experiencing smoother builds, automatic asset fingerprinting, and smaller AOT outputs. This step-by-step guide walks you through the process—from updating your project files to handling advanced packaging strategies like hybrid JIT/AOT engines—so you can leverage the latest improvements with minimal friction.

What You Need

• .NET 10 SDK (preview or stable) installed on your development machine.
• An existing .NET 8 WebAssembly application (e.g., Blazor WebAssembly) with a .csproj file.
• Familiarity with .NET WASM fundamentals (build, publish, load in browser).
• Optional: A WebWorker hosting environment if you run the .NET runtime inside a worker.
• Access to your NuGet package feeds to update dependencies.

Step-by-Step Upgrade Process

1. Update the Target Framework

   Open your .csproj file and change the <TargetFramework> from net8.0 to net10.0. For Blazor WebAssembly apps, also update the Microsoft.AspNetCore.Components.WebAssembly package versions. Example:

   <TargetFramework>net10.0</TargetFramework>
   <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="10.0.0-*" />

   This is the core change that triggers the .NET 10 compiler and runtime.

2. Resolve Dependency Incompatibilities

   Run dotnet restore to see if any NuGet packages are incompatible with .NET 10. Update conflicting packages to versions that support the new runtime. In many cases, simply bumping to the latest stable versions resolves issues. Copilot Studio reported a smooth transition with no major dependency hurdles.

3. Enable Automatic Fingerprinting (Remove Manual Scripts)

   In .NET 10, WASM assets are automatically fingerprinted during publish: each file (e.g., dotnet.js, blazor.boot.json) gets a unique hash in its filename. This provides cache-busting and integrity validation out of the box. If you previously used custom scripts to rename files with SHA256 hashes or passed integrity arguments from JavaScript, you can now delete that code entirely.

   Simply publish as usual (dotnet publish -c Release) and the build output will contain fingerprinted filenames. The runtime automatically validates integrity when loading resources via dotnet.js. Copilot Studio removed a PowerShell renaming script and the integrity argument from their client-side resource loader.

   Tip: If you load the .NET WASM runtime inside a WebWorker, set dotnetSidecar = true when initializing to ensure proper initialization in a worker context.

4. Leverage Smaller AOT Output with WasmStripILAfterAOT

   In .NET 10, the property WasmStripILAfterAOT is enabled by default for AOT builds. After ahead-of-time compiling .NET methods to WebAssembly, the original Intermediate Language (IL) for those methods is stripped, reducing the published output size. If your application uses a pure AOT strategy, this happens automatically—no changes needed.

   However, if you use a hybrid JIT/AOT approach (like Copilot Studio), be aware that stripping IL makes AOT assemblies different from their JIT counterparts. This affects file deduplication strategies (see next step).

   

5. Optimize Hybrid JIT/AOT Packaging (Advanced)

   Copilot Studio ships a single NPM package containing both a JIT engine (for fast startup) and an AOT engine (for maximum execution speed). At runtime, both are loaded in parallel: JIT handles initial interactions, then control hands off to AOT once ready. To keep the package small, files that are bit-for-bit identical between JIT and AOT (like native dependencies) are deduplicated.

   Because WasmStripILAfterAOT removes IL from AOT assemblies, they no longer match their JIT counterparts. This means fewer files can be deduplicated. If you use a similar hybrid approach, review your deduplication logic and accept the slight increase in package size. The performance gains from better AOT optimization outweigh the trade-off for most scenarios.

6. Test and Deploy

   After updating the framework and dependencies, run your application locally with dotnet run or by loading the published output in a browser. Verify that all features work, especially dynamic code loading and WebWorker integration if used. Once testing passes, deploy to your production environment.

Tips for a Smooth Transition

• Backup your current build scripts: Before removing custom fingerprinting or integrity logic, keep a copy in case you need to roll back.
• Monitor file sizes: Check the published output for unexpected increases, especially if you use hybrid JIT/AOT. The reduction from stripping IL should offset some overhead.
• Use the latest preview: .NET 10 is still in development; test with the latest preview SDK to catch breaking changes early.
• Review caching policies: Automatic fingerprinting means your CDN or server cache may behave differently. Ensure your cache headers consider the new filenames.
• Engage the community: Check the .NET WebAssembly GitHub repository for known issues and workarounds related to .NET 10 upgrades.
• Consider a gradual rollout: Deploy the upgraded version to a subset of users first to validate performance and stability.

By following these steps, you’ll harness the power of .NET 10 for WebAssembly—faster startup, smaller downloads, and a simpler deployment pipeline. Copilot Studio’s success proves that the migration is straightforward and delivers measurable improvements. Start planning your upgrade today!

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