MCP 2026-07-28 Spec Drops Sessions, Makes Servers Stateless HTTP Services

The Model Context Protocol released its most significant update on July 28, 2026, eliminating the session handshake and the Mcp-Session-Id header so every request is now fully self-describing. The change means MCP servers can run as plain stateless HTTP services, enabling standard round-robin load balancing, autoscaling, and caching without sticky sessions. A new mechanism called MRTR allows tools to request user input mid-call by returning a closed response with an 'input_required' status, then resuming when the client retries with answers attached. Tool and resource list responses now support caching via ttlMs and cacheScope fields, reducing redundant fetches from clients. Three features — Roots, Sampling, and Logging — are deprecated alongside the legacy HTTP+SSE transport, with at least 12 months of continued support before removal.
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