Python SDK 2.2.0 and 1.30.0 restrict HTTP redirects and expire idle Streamable HTTP sessions

The official Python SDK released v2.2.0, on the 2.x line, and v1.30.0, on the 1.x line, both on 2026-09-07. The two release bodies describe matching behavior changes shipped to both lines. The HTTP client (Client, streamable_http_client, and sse_client on 2.x; streamable_http_client and sse_client on 1.x) now follows a redirect "only if it stays on the same scheme, host and port," or an http-to-https upgrade on the same host; a redirect elsewhere fails the request instead (MCPError on 2.x, httpx.HTTPStatusError on 1.x). The follow_redirects setting on a caller-supplied HTTP client is no longer used for MCP requests, and the OAuth providers apply the same origin rule to their own requests.

Both lines now expire idle Streamable HTTP sessions. A stateful session idle for 30 minutes is closed, and the client's next request gets a 404 and must reinitialize; a server also caps concurrent sessions at 10,000, returning 503 beyond that. session_idle_timeout and max_sessions turn either limit off (mcp.run() and related entry points on 2.x, FastMCP(...) on 1.x). The 2.x notes add that clients holding the GET stream open, and stateless servers or 2026-07-28 connections, are not affected. Both lines also make the OAuth client validate the authorization server's issuer on discovery: 2.x extends a check already applied via protected resource metadata since 2.0 to the legacy path as well (#3398), while 1.x rejects a mismatched issuer outright and re-registers the client if the server later points at a different authorization server (#3431). Both add AuthSettings.validate_token_resource, to accept only tokens the configured TokenVerifier reports as issued for that server, and an issuer= parameter on ClientCredentialsOAuthProvider and PrivateKeyJWTOAuthProvider, alongside two new deprecation warnings for constructing those without it.

v2.2.0 carries one fix not stated in v1.30.0's release notes: $refs in a tool's outputSchema now resolve within that schema document only, and an unresolvable reference surfaces as RuntimeError: Invalid schema for tool ... (#3394). v2.2.0 also closes session-cleanup gaps where a client DELETE did not free its session immediately and a refused opening request could leave one behind (#2455, #3228, #3300).