MCP Goes Stateless: Beta SDKs for the 2026-07-28 Spec Revision
Source: Model Context Protocol Blog — published June 29, 2026
Summary
The MCP maintainers shipped beta SDKs (Python, TypeScript, Go, C#) implementing the upcoming 2026-07-28 spec revision, the largest protocol change since MCP launched. The headline change removes the initialize handshake and Mcp-Session-Id header entirely, making the core protocol stateless: clients now send protocol version and capabilities in _meta on every request, so any server instance can handle any request without sticky routing or a shared session store. The revision also introduces Multi Round-Trip Requests (MRTR), letting a tool return InputRequiredResult to ask the user something mid-call, plus routable transport headers and tightened authorization. The maintainers are explicit that "nothing breaks today, and nothing breaks on July 28 either" — old and new protocol versions can interoperate during the transition.
Key Takeaways
- Stateless-by-default architecture: dropping the handshake means a remote MCP server can now sit behind a plain round-robin load balancer instead of needing sticky sessions or a shared session store — a real operational simplification for anyone running MCP servers at scale.
- SDK v2 breaking changes are real, even if the wire protocol isn't forced: Python's v2 replaces
FastMCPwithMCPServer; TypeScript v2 splits the monolithic package into focused libraries like@modelcontextprotocol/server. Go and C# get gentler migration paths. - MRTR (Multi Round-Trip Requests) formalizes mid-call user input — a tool call can pause and ask a clarifying question via
InputRequiredResultinstead of failing or guessing, closing a common gap in today's tool-calling UX. - Backward compatibility is a stated design goal: clients/servers on different protocol versions can interoperate through the July 28 cutover, so existing deployments aren't forced into a hard migration window.
- Timeline: betas are out now for production testing and feedback; the spec finalizes July 28, 2026.