.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.
Libraries: Process, Compression, and System.Text.Json
The Process API received its biggest expansion in years. New additions include run-and-capture helpers, fire-and-forget launch support, SafeProcessHandle lifecycle methods, and tighter handle control.
System.IO.Compression gains native Zstandard support and CRC32 validation when reading ZIP entries. System.Text.Json adds JsonNamingPolicy.PascalCase, per-member naming policy overrides, type-level ignore conditions, and F# discriminated union support.
SDK, ASP.NET Core, and C# 15
dotnet watch gains Aspire app-host integration, automatic crash recovery, and device selection for MAUI and mobile projects. dotnet run adds a -e flag for passing environment variables from the CLI. CLI telemetry migrates from Application Insights to OpenTelemetry. An MCP Server project template ships with the SDK.
In ASP.NET Core, Blazor gains the SupplyParameterFromTempData attribute and server-initiated circuit pause for Blazor Server. Generated OpenAPI documents now include HTTP QUERY support.
C# 15 brings collection expression arguments and union types. In EF Core, JSON column mapping is treated as a first-class citizen in the relational model with structured JSON path representation. Approximate vector search is available for SQL Server 2025. The dotnet ef tool reads default option values from a .config/dotnet-ef.json file, with discovery walking up parent directories similarly to .editorconfig.
Final thoughts
Preview 4 consolidates the path toward the November 2026 final release. Stable Runtime Async, native Zstandard, and the Process API expansion are the changes with the most immediate impact for most projects. Teams using MAUI or integrating with SQL Server 2025 for vector search will also find the dotnet watch device selection and EF Core's approximate vector search worth evaluating early.
Which of these changes are you planning to try first in your project?
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