Microsoft has released MCP C# SDK v2.0, a major update of the company’s official C# SDK for Model Context Protocol (MCP) servers and clients.
Unveiled July 28, MCP C# SDK v2.0 implements the 2026-07-28 revision of the MCP specification, which Microsoft described as the protocol’s largest revision since its launch. The 2026-07-28 revision makes the MCP protocol stateless by default, standardizes the HTTP surface to allow ordinary HTTP infrastructure to route MCP traffic, and introduces Multi Round-Trip Requests (MRTR) to support interaction without requiring long-lived sessions.
MCP C# SDK 2.0 moves in lockstep with these changes, Microsoft said. The HTTP server transport now runs statelessly by default. Whereas version 1.x of the SDK configured stateful sessions out of the box, in version 2.0 HttpServerTransportOptions.Stateless defaults to true.
MCP C# SDK v2.0 also implements a small set of HTTP headers that the 2026-07-28 MCP revision standardizes. A tools/call now includes Mcp-Method: tools/call and Mcp-Name: get_order_status alongside the JSON-RPC body. With the 2026-07-28 revision, an MCP request becomes a single, self-describing HTTP POST. This means that ordinary HTTP infrastructure such as load balancers, proxies, gateways, and web application firewalls now can act on MCP traffic without deep packet inspection, Microsoft said.
