{
  "id": 7500283,
  "title": "Microsoft Releases .NET 11 RC1 with Go-Live Support, C# 15 and F# 11 as Default Language Versions",
  "url": "https://urgent.news/2026/09/15/microsoft-releases-net-11-rc1-with-go-live-support-c-15-and-f-11-as",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-09-15T07:11:00.000Z",
  "source": {
    "name": "InfoQ",
    "slug": "infoq",
    "url": "https://www.infoq.com/news/2026/09/dotnet-11-rc-1-release/"
  },
  "original_language": "en",
  "account": "Microsoft has unveiled its latest release, .NET 11 RC1, accompanied by the introduction of C# 15 and F# 11 as the default language versions. This Release Candidate 1 version is now go-live supported, allowing teams to incorporate it into production applications. The announcement reveals that .NET 11 RC1 finds compatibility with the upcoming Visual Studio 2026 Insiders release and Visual Studio Code equipped with the C# Dev Kit.\n\nAmong the key enhancements in .NET 11 RC1 are the stabilization of features introduced during the preview cycle. These include the stabilization of collection expression arguments, union types, non-virtual static interface members, closed class hierarchies, labeled break and continue, and extension indexers. Notably, union types are no longer dependent on the preview language setting. The Roslyn compiler now utilizes the final CSharp15 names, and a new API is introduced to expose the cases of a union to analyzers. The RC1 edition maintains the safety of the Unsafe Evolution feature through an optional flag and permits the use of await within an unsafe context.\n\nF# 11 has also been designated as the default language version in this release, featuring stabilized record spreads and direct delegate construction. The string interpolation has been optimized to compile to String.Concat rather than the former reflection-based printf engine, enhancing compatibility with trimming and Native AOT. Additional features comprise reflection-free ToString output for records and unions, support for inheritdoc and include documentation tags, and the introduction of a new Async.RunSynchronouslyImmediate function.\n\nIn terms of the Software Development Kit (SDK), .NET 11 RC1 allows for the testing of projects targeting Android, iOS, macOS, and Mac Catalyst. The SDK offers new project templates for each platform, along with run-level options to set a timeout, halt a run after a number of failures, and assign each test application a unique results directory. The container publishing process now produces the same image digest across builds when the SOURCE_DATE_EPOCH is specified, further streamlining the development process. Finally, ASP.NET Core finalizes the SignalR authentication refresh APIs for both the server and the .NET client, extending similar support to the TypeScript client.",
  "summary": "Last week, Microsoft has released .NET 11 Release Candidate 1, the first release candidate of the cycle, shipping with a go-live support license for production use. The release makes C# 15 and F# 11 the default language versions, extends dotnet test to mobile and desktop targets, finalizes the SignalR authentication refresh APIs, and improves Android build times in .NET MAUI. By Almir Vuk",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}