model context protocol goes stateless in its 2026-07-28 spec

what happened

• On December 9, 2025 Anthropic donated MCP to the Agentic AI Foundation, a directed fund under the Linux Foundation co-founded by Anthropic, Block and OpenAI, with Block's goose and OpenAI's AGENTS.md as fellow founding projects.[1,2]
• Anthropic said at the time there were more than 10,000 active public MCP servers and 97M+ monthly SDK downloads across Python and TypeScript, and that ChatGPT, Cursor, Gemini, Microsoft Copilot and Visual Studio Code had adopted MCP.[1]
• The MCP blog announced the 2026-07-28 specification on July 28, 2026, saying MCP 'is transforming from a bidirectional stateful protocol into a request/response stateless protocol.'[3]
• The revision removes the initialize handshake and the Mcp-Session-Id header; every request carries its protocol version and client capabilities, and servers must implement a new server/discover method.[4]
• It deprecates the Roots, Sampling and Logging features and OAuth Dynamic Client Registration (in favor of Client ID Metadata Documents), and reclassifies the HTTP+SSE transport, deprecated since 2025-03-26, as Deprecated under a new feature lifecycle policy with a minimum twelve-month deprecation window.[4]
• Clients must now validate a present iss parameter per RFC 9207 and must not reuse stored client credentials with a different authorization server.[4]
• The TypeScript, Python, Go and C# SDKs (Tier 1) support 2026-07-28 and Rust is in beta; the post warns of migration cost 'especially for developers that did depend on session identifiers.'[3]