Microsoft unveils first preview of .NET 11

Microsoft has released .NET 11 Preview 1, a planned update to the cross-platform software development platform that features JIT performance improvements, faster compression, CoreCLR support onWebAssembly, and a host of other capabilities.

Unveiled February 10,  the preview can be downloaded from dotnet.microsoft.com. Improvements cover areas ranging from the runtime and libraries to the SDK, the C# and F# languages, ASP.NET Core and Blazor, and .NET MAUI (Multi-platform App UI). Changes to the JIT compiler focus on improving startup throughput, enabling more optimizations, and reducing overhead in key code patterns. The enhancements include raising the multicore JIT MAX_METHODS limit to better support large workloads and improve startup throughput in method-heavy apps. Also, non-shared generic virtual methods are de-virtualized to reduce virtual-call overhead and enable further inlining/optimization opportunities. The JIT also generalizes pattern-based induction-variable (IV) analysis to enable more loop analysis cases, opening the door to more loop optimizations, according to Microsoft.

Additionally in .NET 11, initial work has been done to bring CoreCLR support to WebAssembly, although this feature is not yet ready for general release in Preview 1. As part of this work, .NET 11 Preview 1 begins bringing up a Wasm-targeting RyuJit that will be used for AOT compilation. .NET WebAssembly is being migrated from the Mono runtime to CoreCLR.

Zstandard compression support in .NET libraries in .NEt 11 means significantly faster compression and decompression compared to existing algorithms while maintaining competitive compression ratios. New APIs include a full set of streaming, one-shot, and dictionary-based compression and decompression capabilities. Also featured is a per-year cache for time zone transitions, improving performance for time conversions. The cache stores all transitions for a given year in UTC format, eliminating repeated rule lookups during conversions.

C# 15 in .NET 11 Preview 1 introduces collection expressions arguments, a feature that supports scenarios where a collection expression does not produce the desired collection type. Collection expression arguments enable developers to specify capacity, comparers, or other constructor parameters directly within the collection expression syntax. C# 15 also brings extended layout support, by which the C# compiler emits the TypeAttributes.ExtendedLayout for types that have the System.Runtime.InteropServices.ExtendedLayoutAttribute applied. This feature is primarily intended for the .NET runtime team to use for types in interop scenarios.

With F# 11 in .NET 11 Preview 1, the F# compiler has parallel compilation enabled by default and features faster compilation of computation expression-heavy code. ML compatibility has been removed, though. The keywords asr, land, lor, lsl, lsr, and lxor — previously reserved for ML compatibility — are now available as identifiers. Microsoft said that F# began its life as an OCaml dialect running on .NET, and for more than two decades, the compiler carried compatibility constructs from that heritage including .ml and .mli source file extensions, the #light "off" directive for switching to whitespace-insensitive syntax, and flags like --mlcompatibility. These served the language well during its early years, providing a bridge for developers coming from the ML family, the company said, but that chapter comes to a close. About 7,000 lines of legacy code have been removed across the compiler, parser, and test suite.

.NET 11 follows the November 2025 release of .NET 10, which brought AI, language, and runtime improvements. Other features touted for .NET 11 include the following:

• Runtime async introduces new runtime-level infrastructure for async methods. The goal is to improve tools and performance for async-heavy codepaths.
• CoreCLR is now the default runtime for Android Release builds. This should improve compatibility with the rest of .NET as well as reduce startup times, Microsoft said.
• CLI command improvements in the SDK include dotnet run being enhanced to support interactive selection workflows, laying the foundation for improved .NET MAUI and mobile development scenarios.
• The Blazor web framework adds an EnvironmentBoundary component for conditional rendering based on the hosting environment. This component is similar to the MVC environment tag helper and provides a consistent way to render content based on the current environment across both server and WebAssembly hosting models, Microsoft said.
• XAML source generation is now the default in .NET 11 for all .NET MAUI applications, improving build times, debug performance, and release runtime performance. Debug build app behavior is consistent with release build app behavior, according to Microsoft.