MCP drops sessions in its July 2026 spec

Claim

Any MCP server written against the 2025 spec (sessions, initialize, server-pushed sampling or elicitation, SSE resumability) is now on a deprecated path. The 2026-07-28 revision moved MCP to request-response so "any instance can serve any request", and adoption jumped after it.

Evidence

• Protocol-level sessions and Mcp-Session-Id removed; initialize handshake removed; every request carries version and client capabilities in _meta; mandatory server/discover; Streamable HTTP POSTs carry Mcp-Method and Mcp-Name for gateway routing; SSE resumability removed.
• Server-initiated sampling, elicitation and roots replaced by Multi Round-Trip Requests: the server returns resultType: "input_required" and the client retries with inputResponses. Roots, Sampling and Logging are deprecated with a 12-month window; migration advice is to call the LLM provider directly instead of Sampling. HTTP+SSE transport deprecated.
• Tasks moved to the io.modelcontextprotocol/tasks extension with tasks/get polling and tasks/update; subscriptions/listen is the one long-lived stream for change notifications.
• Auth: Dynamic Client Registration deprecated in favour of Client ID Metadata Documents; iss validation required; credentials bound to the issuing authorisation server.
• tools/list and friends must return ttlMs and cacheScope; servers should return tools in deterministic order to protect prompt caches.
• MCP Apps (interactive UI in a sandboxed iframe) is the first official extension, live 2026-01-26 in Claude, ChatGPT, VS Code and Goose.
• Adoption: Tier-1 SDKs near half a billion downloads per month; ChatGPT MCP tool calls 98x from January to August 2026. The MCP Registry is still in preview (software v1.8.1, August 2026); no GA announcement found. UNVERIFIED.
• Roadmap (2026-08-22): webhooks and triggers, HTTP over stdio, agent identity (DPoP, workload identity federation), server-side progressive discovery so clients stop ingesting the whole catalogue.

Open questions

• Whether SDK 2.x clients can still reach a 1.x stateless server during the deprecation window, or whether the handshake removal breaks it.

Sources

• https://modelcontextprotocol.io/specification/2026-07-28/changelog — spec, Mon Jul 27
• https://blog.modelcontextprotocol.io/posts/2026-07-28/ — blog, Mon Jul 27
• https://modelcontextprotocol.io/development/roadmap — docs, Fri Aug 21
• https://aaif.io/blog/mcp-usage-surged-as-the-protocol-went-stateless — blog, Mon Aug 31
• https://blog.modelcontextprotocol.io/posts/2026-01-26-mcp-apps/ — blog, Sun Jan 25
• https://py.sdk.modelcontextprotocol.io/migration/ — docs, Mon Jul 27

AI-assisted research: gathered and summarised with AI from the sources above, each claim checked against them.