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Sep 4, 2026 · Backend Development

C# 15 Preview Adds Union Types, Closed Hierarchies, and Expanded Unsafe Keyword

Microsoft's C# 15 preview introduces union types for compiler-verified type combinations, closed hierarchies to restrict inheritance, an expanded unsafe keyword for stricter memory safety, plus collection expression parameters, indexers in extensions, and labeled break/continue statements, all shipping with .NET 11 in November.