What’s New in .NET 11 Preview and C# 15? Key Features and Runtime Changes
Microsoft’s .NET 11 preview introduces two‑year STS support, reduces reliance on the Mono runtime, promotes CoreCLR for WebAssembly and Android, adds Zstandard compression, and unveils C# 15 collection‑expression arguments, offering developers early access to significant performance and language enhancements.
.NET 11 preview and support policy
Microsoft released the first preview of .NET 11 and C# 15, marking the initial phase of the 2026 release cycle. General Availability is scheduled for November 2026. .NET 11 will be covered by a two‑year Standard Term Support (STS) lifecycle.
Mono runtime deprecation
The preview continues the effort to replace the Mono runtime, which originated from the Xamarin acquisition. Mono remains the runtime for MAUI‑based mobile apps and WebAssembly, but in .NET 11 the CoreCLR runtime becomes the target library for the .NET WebAssembly SDK and is the default runtime for Android builds (previously experimental in .NET 10). This reduces the platform’s reliance on Mono.
Library enhancements
Native support for Zstandard (zstd) compression, delivering measurable performance gains for compression‑related APIs.
C# 15 collection‑expression arguments
C# 15 introduces collection‑expression arguments, enabling developers to customize collection creation directly in an initializer. Example:
list<string> names = [with(capacity: values.Count * 2), ..values];Details of the proposal are available at https://github.com/dotnet/csharplang/blob/main/proposals/collection-expression-arguments.md
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