.NET 11 Preview 4: Stable Runtime Async, Native Zstandard, and Union Types in C# 15

.NET 11 Preview 4: Stable Runtime Async, Native Zstandard, and Union Types in C# 15

The .NET Blog published .NET 11 Preview 4 in May 2026. The final release is expected in November 2026. This post walks through the most relevant changes for .NET developers.

Runtime Async and JIT

The most significant runtime change is the stabilization of Runtime Async. Starting with Preview 4, projects targeting net11.0 no longer need <EnablePreviewFeatures>true</EnablePreviewFeatures>. According to the .NET Blog, the runtime libraries themselves are compiled with runtime-async=on, delivering cleaner stack traces and lower async overhead.

On the JIT side, improvements cover bounds check elimination, redundant checked context removal, switch expression folding, constant-folding of SequenceEqual, and new Arm SVE2 intrinsics for supported hardware.