MCP went stateless: What changed in the 2026-07-28 spec

MCP’s 2026-07-28 specification revision shifts the protocol to a stateless, HTTP-like model by removing protocol sessions, the initialize handshake, stream resumability, ping, and logging/setLevel, allowing requests to be handled by any server instance without sticky routing or shared session storage. Requests now carry protocol version, client capabilities, and identity metadata individually, while servers must support an optional server/discover endpoint; multi-step application state is expected to use explicit server-issued handles passed as tool arguments. The most consequential migration challenges are the loss of SSE stream resumption, which requires clients to retry failed requests and developers to add idempotency protections for side-effecting tools, and the replacement of server-initiated elicitation, sampling, and roots interactions with multi-round-trip requests where clients resubmit calls with collected input. The revision also introduces header-based method and tool routing, cache metadata for list and resource endpoints, subscriptions/listen for change notifications, revised errors, and formal feature deprecation rules. Roots, Sampling, Logging, HTTP+SSE, certain includeContext values, and OAuth Dynamic Client Registration are deprecated, while Client ID Metadata Documents, stronger OAuth issuer validation, and per-issuer credential binding are encouraged. Experimental Tasks has moved into an official extension, and updated Tier 1 SDKs support the revision while preserving compatibility with earlier versions.

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