Microsoft shipped .NET 11 on November 10, 2026, as the headlining release of .NET Conf 2026, its annual virtual developer conference. It's a Standard Term Support (STS) release — two years of patches, not four. .NET 10 remains the Long-Term Support option.
The same day .NET 11 shipped, .NET 8 and .NET 9 both reached end of support. If you're on either, you're out of patch coverage now.
C# 15: Union Types Are Finally Here
The headline language feature is union types in C# 15, which ships as the default language version for net11.0 projects. Unions let you define a type that can be one of several distinct cases, all handled through exhaustive pattern matching. Combined with closed hierarchies — a signal that a type hierarchy is complete and no outside types can extend it — they make modeling domain logic far more explicit and safe.
Union types have been one of the most-requested C# features for years. They bring C# closer to what F#, Rust, Swift, and Kotlin have offered for some time, without requiring a language rewrite. C# 15 also includes a preview of an updated memory-safety-focused unsafe model for lower-level scenarios.
MCP Server Template Out of the Box
The addition that will catch the most attention in AI-adjacent circles: .NET 11 ships a built-in MCP server template. Run dotnet new mcpserver and you get a working skeleton for a Model Context Protocol server, ready to wire into Claude, GitHub Copilot, or any MCP-compatible host. Microsoft.Extensions.AI and the new Microsoft Agent Framework also ship in-box, making .NET 11 the first version with first-class tooling for building AI agents without reaching for external packages.
ASP.NET Core Updates
Web developers get several practical additions in ASP.NET Core:
- Asynchronous validation for minimal APIs and controllers
- OpenAPI 3.2 support, the spec that unified Swagger-style docs with AsyncAPI concepts
- Incremental improvements to Blazor and SignalR
Mobile and Runtime
.NET MAUI now defaults to CoreCLR as its runtime, replacing Mono. That means the same runtime everywhere — desktop, server, and mobile — which simplifies reasoning about performance across platforms. XAML hot reload is incremental now, so only changed files recompile.
At the runtime level, Microsoft reports hundreds of optimizations. The SDK enables a Native AOT-based CLI host by default, shaving startup time for command-line tools. Runtime Async V2 — which moves async suspension out of compiler-generated state machines for cleaner stack traces and better debuggability — remains opt-in preview. It's not default yet, but it's stabilizing.
What to Do Now
If you're on .NET 10 (LTS), no immediate action is required — you have support through late 2028. If you're on .NET 8 or .NET 9, you should start planning a migration. And if you're building something new in 2026, .NET 11 is the most feature-complete version available, even if .NET 10 is the safer long-term bet for production workloads that value patch stability over new features.