v2.2.0

pip install -U mcp. Docs: https://py.sdk.modelcontextprotocol.io/

A few defaults changed in this release. If you run a server or client on 2.x, skim these first:

Behaviour changes

HTTP client redirects are only followed within the endpoint's origin (#3397)

• Client("https://..."), streamable_http_client and sse_client follow a redirect only if it stays on the same scheme, host and port (or upgrades http to https on the same host).
• A redirect anywhere else is not followed: the call fails with MCPError and the session stays usable (an SSE connect fails with httpx2.HTTPStatusError). If that other URL is the server you meant, use it as the endpoint URL.
• The follow_redirects setting on an httpx2.AsyncClient you pass in is no longer used for MCP requests, so you don't need it for the trailing-slash redirect any more.
• The OAuth providers apply the same rule to their own requests.

Idle Streamable HTTP sessions now expire (legacy <=2025-11-25 spec( (#3395)

• A stateful session with nothing in flight for 30 minutes is closed. The client's next request gets a 404 and it has to initialize again.
• Clients that keep the GET stream open (the SDK's Client does) are not affected. Neither are stateless servers or 2026-07-28 connections.
• A server also holds at most 10 000 sessions at once; beyond that, new sessions get a 503.
• To turn either off: mcp.run(transport="streamable-http", session_idle_timeout=None, max_sessions=None) (also on streamable_http_app() and run_streamable_http_async()).

The OAuth client checks the authorization server's issuer on the legacy path too (#3398)

• For servers without protected resource metadata, authorization server metadata whose issuer isn't the server's own origin is now rejected with OAuthFlowError: Authorization server metadata issuer mismatch. The protected-resource-metadata path has done this since 2.0.
• A 403 that isn't an insufficient_scope challenge is returned to the caller instead of retried.
• If protected resource metadata can't be fetched because of a 5xx/429, the flow now stops instead of falling back to the legacy endpoints.

Two new MCPDeprecationWarnings (#3435, #3447)

• ClientCredentialsOAuthProvider / PrivateKeyJWTOAuthProvider without issuer=. Pass your authorization server's issuer URL; 3.0 will require it.
• AuthSettings with resource_server_url set but validate_token_resource unset. Set it to True or False; 3.0 defaults it to True.
• Both keep working as before in 2.x; this mostly matters if your tests turn warnings into errors.

New

• AuthSettings.validate_token_resource: only accept tokens your TokenVerifier reports as issued for this server (#3447).
• issuer= on ClientCredentialsOAuthProvider and PrivateKeyJWTOAuthProvider (#3398).
• session_idle_timeout= and max_sessions= on the Streamable HTTP server entry points (#3395).

Fixes

• A client DELETE frees its session immediately, and a refused opening request no longer leaves a session behind (#2455, #3228, #3300).
• $refs in a tool's outputSchema resolve within that schema only; an unresolvable one surfaces as RuntimeError: Invalid schema for tool ... (#3394).

Known gaps

The tasks extension (SEP-2663), DPoP (SEP-1932) and the jwt-bearer grant are not implemented yet; https://github.com/modelcontextprotocol/python-sdk/blob/main/ROADMAP.md tracks them.

What's Changed

• Gate draft PRs too and rewrite the auto-close comment by @maxisbey in #3378
• Resolve tool output-schema references within the schema document only by @maxisbey in #3394
• Expire idle Streamable HTTP sessions by default and cap concurrent sessions by @maxisbey in #3395
• Validate the authorization server metadata issuer on every discovery path by @maxisbey in #3398
• Deprecate constructing the pre-provisioned OAuth clients without an issuer by @maxisbey in #3435
• Exercise the SEP-2575 stateless probes and SEP-2243 resource/prompt headers in the conformance fixtures by @maxisbey in #3442
• Bump the github-actions group with 6 updates by @dependabot[bot] in #3424
• Move the docs-preview workflow scripts out of the YAML into .github/scripts by @maxisbey in #3446
• Skip automatic docs previews for fork PRs and drop the setup-uv retry steps by @maxisbey in #3445
• Follow redirects only within the MCP endpoint's origin by @maxisbey in #3397
• Bump pymdown-extensions from 11.0 to 11.0.1 by @dependabot[bot] in #3285
• Bump the locked versions of eight dev and test dependencies by @maxisbey in #3449
• Keep following a relative redirect when the endpoint URL carries userinfo by @maxisbey in #3450
• Add AuthSettings.validate_token_resource to check a bearer token's resource by @maxisbey in #3447
• docs: stop presenting the in-memory client as the way to connect by @maxisbey in #3443
• docs: ask for AI disclosure on comments too by @maxisbey in #3459
• docs: refresh translations, and translate pages in parallel by @maxisbey in #3458
• Replace RootModel wrappers with type aliases and TypeAdapter validation by @Kludex in #3470

Full Changelog: v2.1.1...v2.2.0