Issues

• Streamable HTTP notification sends a second response when the session writer is closed

  modelcontextprotocol/python-sdk#3651 · opened on Oct 6, 2026
  1

• MCPServer completion handler returning more than 100 values fails on 2026-07-28 sessions and violates the 100-item limit on 2025-11-25 sessions

  modelcontextprotocol/python-sdk#3649 · opened on Oct 6, 2026

• Tool outputSchema is generated in validation mode, so serialization aliases and computed fields don't match structuredContent

  modelcontextprotocol/python-sdk#3644 · opened on Oct 5, 2026
  1

• Prompt handlers returning UserList are rendered as one text message

  modelcontextprotocol/python-sdk#3643 · opened on Oct 5, 2026

• ServerCapabilities drops unknown keys, so a server can't advertise events for ChatGPT's MCP Events

  modelcontextprotocol/python-sdk#3640 · opened on Oct 3, 2026
  4

• Streamable HTTP client hangs on a null-id JSON-RPC error in a 200 JSON response

  modelcontextprotocol/python-sdk#3639 · opened on Oct 3, 2026
  1

• Streamable HTTP notification triggers duplicate response after HTTP 202

  modelcontextprotocol/python-sdk#3631 · opened on Oct 2, 2026
  2

• SSE: a POST blocks forever (and SIGTERM hangs) when the server lifespan raises after an await

  modelcontextprotocol/python-sdk#3616 · opened on Oct 2, 2026
  2

• Add macos-latest to the CI test matrix

  modelcontextprotocol/python-sdk#3597 · opened on Sep 29, 2026
  1

• Streamable HTTP client retries the standalone GET after a 401, 403, or 405

  modelcontextprotocol/python-sdk#3592 · opened on Sep 28, 2026
  1

• Deploy docs: reused-process runtimes (Lambda) hit the single-use session manager error, but aren't covered

  modelcontextprotocol/python-sdk#3590 · opened on Sep 27, 2026

• DirectoryResource listing uses OS path separators and unstable order

  modelcontextprotocol/python-sdk#3589 · opened on Sep 27, 2026
  1

• Image/Audio format= emits image/jpg, audio/mp3, audio/m4a — unregistered MIME types that disagree with the path= suffix table

  modelcontextprotocol/python-sdk#3585 · opened on Sep 26, 2026
  3

• ClientSessionGroup has no routed read_resource / get_prompt (only call_tool)

  modelcontextprotocol/python-sdk#3579 · opened on Sep 24, 2026
  3

• ClientSessionGroup raises KeyError when connecting a server that exposes no components

  modelcontextprotocol/python-sdk#3578 · opened on Sep 24, 2026
  1

• Make Origin validation opt-in in the app factories (keep Host validation on for localhost)

  modelcontextprotocol/python-sdk#3576 · opened on Sep 24, 2026
  2

• func_metadata raises uncaught PydanticSchemaGenerationError for Iterator/AsyncIterator tool return annotations instead of the unstructured fallback

  modelcontextprotocol/python-sdk#3573 · opened on Sep 23, 2026
  4

• Tool validation errors echo the rejected input value (input_value) — add a masking option or a public validation-error hook

  modelcontextprotocol/python-sdk#3572 · opened on Sep 23, 2026
  7

• OAuthClientProvider: no supported way to override endpoints or customize authorization state generation

  modelcontextprotocol/python-sdk#3570 · opened on Sep 23, 2026
  1

• Client transports/sessions swallow the original exception; applications cannot classify 401/403/429 transport failures

  modelcontextprotocol/python-sdk#3569 · opened on Sep 23, 2026

• POST failure identical to task cancellation in streamable HTTP client

  modelcontextprotocol/python-sdk#3560 · opened on Sep 22, 2026
  2

• [MCPServer] Optional ResourcesAsTools support ala FastMCP

  modelcontextprotocol/python-sdk#3559 · opened on Sep 22, 2026

• Malformed requests get -32602 where JSON-RPC 2.0 requires -32600 (non-Request body) and -32601 (unknown method)

  modelcontextprotocol/python-sdk#3557 · opened on Sep 21, 2026
  1

• Streamable HTTP client treats 404 as terminal instead of re-initializing, as the spec requires

  modelcontextprotocol/python-sdk#3556 · opened on Sep 21, 2026
  2

• Structured tool output: -> bytes return crashes with a generic error on non-UTF-8 payloads instead of returning the advertised base64/binary string

  modelcontextprotocol/python-sdk#3554 · opened on Sep 21, 2026
  4