For the first time, MCP is stateless at the protocol layer. The `Mcp-Session-Id` header is gone, the initialize/initialized handshake is gone, and protocol version plus client capabilities now ride in `_meta` on every request. In practice that means a server can sit behind an ordinary round-robin load balancer with no sticky routing, no shared Redis, no session store to babysit. The maintainers locked this release candidate back in May and set today as the publication date; they're calling it the biggest change to the spec since the project started. There's real migration work behind the headline. Roots, Sampling, and Logging are now deprecated, each on a 12-month clock before removal, and auth tightens: clients must validate the `iss` parameter on authorization responses per RFC 9207 to close the mix-up attacks that have dogged MCP deployments. Two official extensions ship alongside the core — MCP Apps for sandboxed HTML UIs, and a reworked Tasks extension for long-running work, both rebuilt around the stateless model. If you host or build MCP servers, read the migration notes before you upgrade. Silent session removal is exactly the kind of change that breaks a client that assumed sticky state.