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Title: First end-to-end 2026-07-28 stateless tools/call (experimental entry + ClientSession pin) by maxisbey · Pull Request #2910 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: First end-to-end 2026-07-28 stateless tools/call (experimental entry + ClientSession pin) by maxisbey · Pull Request #2910 · modelcontextprotocol/python-sdk

X Title: First end-to-end 2026-07-28 stateless tools/call (experimental entry + ClientSession pin) by maxisbey · Pull Request #2910 · modelcontextprotocol/python-sdk

Description: First end-to-end slice of the 2026-07-28 stateless protocol, plus the interaction-suite era axis turned on so the existing transport-agnostic tests run at the new revision. Part of #2891, #2892, #2893, #2894 (closes none). Server mcp.server._streamable_http_modern — handle_modern_request direct-invocation path (private) StreamableHTTPSessionManager.handle_request branches on MCP-Protocol-Version ∈ MODERN_PROTOCOL_VERSIONS per-request ServerRunner over a SingleExchangeDispatcher (no back-channel; notifications no-op pending the SSE response mode) Client Client, ClientSession, and streamable_http_client() gain protocol_version: str | None pinned to "2026-07-28": born initialized (synthesized InitializeResult, placeholder server_info pending server/discover); initialize() is idempotent; stamps the io.modelcontextprotocol/{protocolVersion,clientInfo,clientCapabilities} envelope on every request; cancel_on_abandon=False pinned to a stateful version: initialize() requests that version instead of LATEST_PROTOCOL_VERSION transport pins MCP-Protocol-Version from the constructor; Mcp-Method/Mcp-Name derived per message; _encode_header_value Base64-sentinel-wraps RFC-7230-unsafe names MODERN_PROTOCOL_VERSIONS constant in mcp.shared.version Types CacheableResult defaults to ttl_ms=0, cache_scope="private" so list/read results constructed without explicit hints validate against the 2026-07-28 surface and never accidentally enable shared caching Interaction suite SPEC_VERSIONS = ("2025-11-25", "2026-07-28") — node ids gain a -version suffix the connect fixture forwards protocol_version through Client; in-memory and streamable-http-stateless era-locked to 2025-11-25 [streamable-http-2026-07-28]: 60 pass, 8 xfail (xfails are progress/logging — handler-emitted notifications not yet streamed on the single-exchange path) 13 lifecycle:* requirements get removed_in="2026-07-28"; 6 error-shape requirements excluded (modern-error-surface — tests pin the legacy code=0 divergence; the modern arm returns the spec-correct -32603) the wire contract (envelope, headers, no handshake, no session-id) stays pinned by transports/test_hosting_http_modern.py Conformance 23 scenarios now pass at the 2026-07-28 wire across the draft and carried-forward legs tools-call-with-progress stays expected-fail (progress delivery on the single-exchange path) Behaviour changes ClientSession.initialize() is now idempotent: a second call returns the cached result (or the synthesized one for a stateless pin) instead of re-sending the handshake. All other 2026 behaviour is opt-in via protocol_version=. SUPPORTED_PROTOCOL_VERSIONS and LATEST_PROTOCOL_VERSION are unchanged. Flagged for review 2× # type: ignore[call-arg] in server/session.py for _related_request_id (TODO at :94 — fix is the ServerSession/Context rework) 2× # type: ignore[reportPrivateUsage] in the modern entry (_compose_on_request, _EXIT_STACK_CLOSE_TIMEOUT) — both fall out of the ServerRunner driver-split Out of scope server/discover, _meta validation ladder, version negotiation, subscriptions/listen, MRTR, SSE response mode for the modern entry, public design of the new HTTP path, in-memory modern entry. AI Disclaimer

Open Graph Description: First end-to-end slice of the 2026-07-28 stateless protocol, plus the interaction-suite era axis turned on so the existing transport-agnostic tests run at the new revision. Part of #2891, #2892, #2...

X Description: First end-to-end slice of the 2026-07-28 stateless protocol, plus the interaction-suite era axis turned on so the existing transport-agnostic tests run at the new revision. Part of #2891, #2892, #2...

Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/2910

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