Microsoft has released .NET 11 and C# 15. The headline language feature is union types, something developers have been asking for over a decade. You can now declare that a value is one of a fixed set of types, and the compiler checks that every case is handled in a switch. Forget a new case and you get a build warning instead of a production bug. The second big change is Runtime Async: async methods are now handled by the runtime itself instead of hidden state machines generated by the compiler. Stack traces are cleaner, and a two-level async chain that completes synchronously went from 21 ns to 6 ns and no longer allocates memory.