Metalama November 2025 Update: Release Candidate for Metalama 2026.0

This article was first published on the Metalama Blog.

Ready to try it? The RC packages are available on NuGet.org, and the Visual Studio extension can be downloaded from the Metalama 2026.0 downloads page.

This article covers what we shipped this month. For the complete list of changes in Metalama 2026.0, see the release notes.

For the full list of fixes and enhancements, see the changelogs:

• 2026.0.4-preview (November 8).
• 2026.0.5-preview (November 12).
• 2026.0.6-rc (November 28).

C# 14 Extension Members

This month, we completed support for C# 14 extension blocks. You can now advise extension members and introduce members into existing extension blocks.

Extension blocks are the “extend everything” feature in C# 14. Here’s how Metalama models them:

• Extension blocks use the IExtensionBlock interface, which implements INamedType (TypeKind = Extension) so you can discover members the usual Fields, Properties, Methods, … collections.
• They appear under INamedType.ExtensionBlocks.
• Extension methods and property accessors are also listed in INamedType.Methods as implicitly-implemented methods.
• You can override extension members using the advising API or add aspects using custom attributes.
• You can also add new extension members to existing extension blocks.
• Introducing new extension blocks won’t be supported in 2026.0.

Other Improvements

Single-file applications. Metalama aspects now work in single-file dotnet run applications: arguably a niche scenario.

Toast notifications. Product briefs and news now appear via toast notifications on Windows. You can disable or configure this feature through the UI or CLI tool.

Visual Studio Tools improved stability and performance

During the last two weeks, we focused heavily on Visual Studio extension stability — and uncovered more issues than expected.

We owe you an apology. Most of these bugs were already present in the 2025.1 release, though some may have been introduced by a Visual Studio 17.x minor update (we don’t repeat our full manual test suite after each VS release, so we can’t be certain). We discovered them through exhaustive testing on clean virtual machines as part of our RC validation process.

This level of testing clearly wasn’t done properly for 2025.1. To ensure quality meets our standards, we chose to delay the release by one month, missing our target to reach GA before the Christmas break. It was the right call.

The good news: the Visual Studio extension is now significantly more stable, and we achieved impressive performance improvements along the way. You can download it from the Metalama 2026.0 downloads page.

Known Issues

A couple of items to address before GA:

• There’s a known issue (#149) with the apt package on Linux. We’re working on a fix.
• The next RC will update to Roslyn 5.0.0 GA (#1212).

What’s Next

With full .NET 10 SDK and C# 14 support (except for by-design limitations documented in the release notes), and a significantly more stable Visual Studio extension, we’re on track for GA on January 5th, 2026.

If you haven’t tried the RC yet, now is the time. Test it with your projects and let us know what you find—your feedback helps ensure a rock-solid release.

Happy meta-programming!

-gael