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.NET Runtime in .NET 11 Preview 3 - Release Notes

.NET 11 Preview 3 includes new runtime features and performance work:

.NET Runtime updates in .NET 11:

Runtime async removes the preview-API opt-in requirement

Runtime async still uses the runtime-async=on feature switch, but Preview 3 removes the [RequiresPreviewFeatures] gate from its APIs. A net11.0 project no longer needs <EnablePreviewFeatures>true</EnablePreviewFeatures> just to enable runtime-async=on (dotnet/runtime #124488).

Support for NativeAOT and ReadyToRun also landed in this preview (dotnet/runtime #123952, dotnet/runtime #124203, dotnet/runtime #125420). Follow-on work reuses continuation objects more aggressively and avoids saving unchanged locals, which reduces allocation pressure in async-heavy code (dotnet/runtime #125556, dotnet/runtime #125615).

 <PropertyGroup>
   <Features>runtime-async=on</Features>
-  <EnablePreviewFeatures>true</EnablePreviewFeatures>
 </PropertyGroup>

JIT optimizations improve switches, bounds checks, and casts

Preview 3 continues the steady JIT work that benefits normal code without any source changes. Common patterns like multi-target switch expressions now fold into simpler branchless checks (dotnet/runtime #124567), index-from-end access can drop more redundant bounds checks (dotnet/runtime #124571), and uint to float / double casts are faster on pre-AVX-512 x86 hardware (dotnet/runtime #124114).

Supporting compiler work lets the JIT apply these reductions across more real-world code.

bool isSmall = x is 0 or 1 or 2 or 3 or 4;
int tail = values[^1] + values[^2];
double d = someUint;

Browser and WebAssembly add WebCIL and debugging improvements

Preview 3 expands the browser/CoreCLR work with WebCIL payload loading (dotnet/runtime #124758, dotnet/runtime #124904), better symbols and stack traces for debugging (dotnet/runtime #124500, dotnet/runtime #124483), and marshal float[], Span<float>, and ArraySegment<float> more directly across JS boundaries (dotnet/runtime #123642).

Breaking changes

  • NativeAOT native-library outputs now use the conventional lib prefix on Unix. If your scripts expected MyLib.so, update them to look for libMyLib.so (dotnet/runtime #124611).

Bug fixes

Community contributors

Thank you contributors! ❤️