TimelineC# 15

C# 15

Union Types, Closed Hierarchies & Extension Indexers

Introduced first-class union types, closed class hierarchies, extension indexers, collection expression arguments, and labeled break and continue.

November 2026
.NET 11.0
Visual Studio 2026
C# language design team

Historical Context

Shipped with the .NET 11 SDK, a Standard Term Support release, to make exhaustive pattern matching a language feature and extend extension members to indexers.

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C# 14

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