MCP C# SDK v2.0 implements the 2026-07-28 MCP specification, the largest protocol revision since launch. Key changes include stateless-by-default HTTP transport (eliminating sticky sessions and enabling horizontal scaling), standardized HTTP headers (Mcp-Method, Mcp-Name, Mcp-Param-*) for routing MCP traffic without body inspection, and Multi Round-Trip Requests (MRTR) that allow interactive tools to request user input without persistent sessions. MRTR replaces the old server-initiated elicitation, sampling, and roots patterns. The release is backward compatible — v1 code continues to compile, old clients/servers still work, and deprecated APIs emit warnings rather than errors. The SDK targets net8.0, net9.0, net10.0, and netstandard2.0, and ships as composable NuGet packages. Extensions for long-running Tasks and server-delivered Apps are opt-in separate packages. Next focus is end-to-end authentication and authorization.
