Copilot Studio's Leap to .NET 10 on WebAssembly: A Q&A Guide

Welcome to our deep dive into how Microsoft Copilot Studio turbocharged its performance by moving from .NET 8 to .NET 10 on WebAssembly. In this Q&A, we explore the seamless upgrade process, the game-changing automatic fingerprinting feature, and how smaller AOT builds reduce payload size—without sacrificing speed. Whether you're a developer optimizing your own WASM app or just curious about the tech behind Copilot Studio, these questions and answers cover everything you need to know.

1. How did Copilot Studio upgrade from .NET 8 to .NET 10 on WebAssembly?

The upgrade was remarkably straightforward. The team simply updated the target framework in their .csproj files from net8.0 to net10.0 and verified all dependencies were compatible with .NET 10. No major code rewrites or architectural changes were needed. Once the build passed, they deployed the new .NET 10 WASM engine directly to production. This smooth transition highlights the backward compatibility and incremental improvement philosophy of the .NET team. For developers managing similar projects, it’s reassuring to know that moving to the latest .NET version for WASM can be as simple as a version bump in your project file, followed by thorough testing of your asset pipeline and runtime behavior.

2. What is automatic fingerprinting and why does it matter for WASM apps?

Automatic fingerprinting is a new feature in .NET 10 that appends a unique identifier to each published WASM asset’s filename. This solves two critical problems: cache busting and integrity validation. Previously, Copilot Studio had to manually read the blazor.boot.json manifest, run a custom PowerShell script to rename files with SHA256 hashes, and pass explicit integrity arguments from JavaScript. With .NET 10, all of that manual work disappears. The dotnet.js runtime automatically imports resources with fingerprint-based names, and integrity checks happen transparently. The team was able to delete their custom renaming script and remove the integrity argument from the client-side loader, simplifying deployment and reducing the risk of errors. Existing caching and validation logic on top of these resources continued to work without modification.

3. How does automatic fingerprinting improve deployment for Copilot Studio?

By eliminating the manual fingerprinting steps, Copilot Studio’s deployment pipeline became leaner and more reliable. The PowerShell script that used to rename files is gone, and the JavaScript resource loader no longer needs to supply explicit integrity hashes. This not only reduces code complexity but also speeds up the build process. Because fingerprints are now generated at publish time and embedded in filenames, the team can push updates with confidence that browsers will fetch the latest assets immediately (cache busting) and that tampered files will be rejected (integrity). The change also plays nicely with content delivery networks (CDNs) and edge caching, since each unique version of a file gets its own URL. For a large-scale service like Copilot Studio, these small optimizations add up to faster, safer rollouts.

4. What is WasmStripILAfterAOT and how does it reduce output size?

After ahead-of-time (AOT) compilation, .NET methods are translated directly to WebAssembly, making the original Intermediate Language (IL) unnecessary at runtime. In .NET 10, the property WasmStripILAfterAOT is now enabled by default for AOT builds, which strips that IL from the published output. This reduces the total download size for end users, especially for applications that ship a pure AOT engine. In .NET 8, this setting existed but defaulted to false, so most apps carried extra IL bytes. Copilot Studio uses a hybrid approach: it ships both a JIT engine (for fast startup) and an AOT engine (for peak performance). Because stripping IL makes AOT assemblies different from their JIT counterparts, fewer files can be deduplicated between the two modes—but the trade-off is worth it for smaller AOT payloads and faster load times once AOT takes over.

5. How does Copilot Studio manage parallel loading of JIT and AOT engines?

Copilot Studio packages both a JIT engine and an AOT engine inside a single NPM package. At runtime, both engines are loaded in parallel. The JIT engine starts executing first, providing immediate responsiveness while the AOT engine continues to compile in the background. Once the AOT engine is fully ready, control gracefully transitions from JIT to AOT for maximum execution speed. Files that are bit-for-bit identical between the two modes are deduplicated to minimize download size. This strategy gives users the best of both worlds: snappy initial interactions (thanks to JIT) and sustained high performance (thanks to AOT). The upgrade to .NET 10 further improved this by making AOT builds smaller via WasmStripILAfterAOT, though it slightly reduces the number of deduplicatable files.

6. Are there any special considerations for running .NET WASM in a WebWorker?

Yes. If you load the .NET WASM runtime inside a WebWorker, you need to set dotnetSidecar = true when initializing the runtime. This ensures proper initialization in a worker context, where global objects like window are not available. Copilot Studio does not use WebWorkers for its main copilot interactions, but this tip is invaluable for developers building multi-threaded WASM applications that offload heavy computation to background threads. Neglecting this flag can lead to runtime errors or unexpected behavior. The Copilot Studio team documented this setting as a best practice for anyone customizing their WASM deployment beyond the standard browser main thread scenario.

7. What performance gains did Copilot Studio measure after moving to .NET 10?

While the original post didn’t publish specific benchmark numbers for the .NET 10 upgrade, the team previously reported significant gains when moving from .NET 6 to .NET 8—including faster startup times and reduced memory usage. The upgrade to .NET 10 builds on that foundation. The most impactful improvements are automatic fingerprinting (simplifying asset loading and reducing manual steps) and the default WasmStripILAfterAOT (which shrinks AOT payloads). For end users, this translates to quicker first interactions and smoother ongoing experiences within Copilot Studio. Developers can expect similar benefits when updating their own WASM apps: leaner builds, easier deployment, and no regressions in existing functionality. The team continues to measure and optimize, promising even better performance with each .NET iteration.