If you build or operate MCP servers or clients, this release changes the wire contract: stateless self-describing requests, header-based routing, MRTR instead of long-lived streams for sampling/elicitation, and a shift from Dynamic Client Registration to client metadata documents.
The 12-month deprecation window tells you exactly how long your current stateful implementation has.
This release of the Model Context Protocol overhauls the protocol into a stateless request/response core, removing the initialize handshake and session IDs in favor of self-describing requests and header-based routing (Mcp-Method, Mcp-Name).
It introduces Multi Round-Trip Requests (MRTR) to replace held-open bidirectional streams for sampling and elicitation, adds cacheable list results, tightens authorization (RFC 9207 issuer validation, a shift from Dynamic Client Registration to client metadata documents), formalizes an extensions framework (including Tasks), and ships updated TypeScript, Python, Go, and C# SDKs with a 12-month deprecation policy.
Transcript
Also in this release:
Auth hardening and a formal deprecation policy
See the MCP blog for more:
https://t.co/ryZR9fAwB8
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