Issues

• notifications/cancelled for request 7 cancels a concurrent request "7" (_in_flight keyed by coerce_request_id)

  modelcontextprotocol/python-sdk#3807 · Filter by author ashirimi1019 opened on Nov 2, 2026

• Server stop hangs while a 2026-07-28 subscriptions/listen stream is open

  modelcontextprotocol/python-sdk#3806 · Filter by author inxbit opened on Nov 2, 2026

• images.py example returns raw pixels from tobytes() labelled image/png, so clients cannot decode the thumbnail

  modelcontextprotocol/python-sdk#3805 · Filter by author chrikrah opened on Nov 2, 2026

• stdio client: requests hang forever after the server closes stdout but keeps running

  modelcontextprotocol/python-sdk#3804 · Filter by author gowthamrao opened on Nov 2, 2026

• Tool results over 1 MiB cannot be received over SSE or streamable HTTP, and the limit is not configurable

  modelcontextprotocol/python-sdk#3803 · Filter by author gowthamrao opened on Nov 2, 2026

• ClientSessionGroup.connect_to_server leaves the caller's task cancelled when an HTTP server is unreachable

  modelcontextprotocol/python-sdk#3801 · Filter by author gowthamrao opened on Nov 2, 2026
  1

• MCP Apps: clientCapabilities from the per-request _meta envelope never reaches handlers on stateless Streamable HTTP — client_supports_apps() is always False

  modelcontextprotocol/python-sdk#3800 · Filter by author Yshmily opened on Nov 2, 2026
  1

• Raise a distinct error when a Streamable HTTP session is lost (HTTP 404)

  enhancement
  modelcontextprotocol/python-sdk#3799 · Filter by author campoy opened on Nov 2, 2026
  1

• ClientSessionGroup silently omits later pages of tools, resources, and prompts

  bugv1v2
  modelcontextprotocol/python-sdk#3792 · Filter by author namtran1812 opened on Oct 31, 2026
  1

• Productive SSE reconnects accumulate stack frames and eventually fail

  bugv1v2
  modelcontextprotocol/python-sdk#3791 · Filter by author namtran1812 opened on Oct 31, 2026

• Windows stdio server: subprocess spawned inside a tool handler hangs forever when it inherits the server stdin (stdin=DEVNULL fixes)

  bugv1
  modelcontextprotocol/python-sdk#3788 · Filter by author dadawalissonsilva opened on Oct 30, 2026
  3

• streamable HTTP: integer and string request ids with the same text share one response stream; a string id can displace the GET stream

  bugv1v2
  modelcontextprotocol/python-sdk#3786 · Filter by author WingedGuardian opened on Oct 29, 2026
  4

• Security: DNS rebinding protection is opt-in, not enabled by default

  enhancement
  modelcontextprotocol/python-sdk#3784 · Filter by author alemaiorano opened on Oct 28, 2026
  3

• OAuth scope selection falls back to the authorization server's scopes_supported, which the spec does not allow

  bugv1v2
  modelcontextprotocol/python-sdk#3781 · Filter by author jin-bo opened on Oct 28, 2026
  2

• Advertise scopes_supported separately from required_scopes

  enhancement
  modelcontextprotocol/python-sdk#3778 · Filter by author tlwns opened on Oct 28, 2026
  1

• Expose optional cache outcome events on the high-level Client

  enhancement
  modelcontextprotocol/python-sdk#3777 · Filter by author Yut0Miura opened on Oct 27, 2026
  5

• [Bug]: Inconsistent structured output wrapping and opt-out for typing.Dict and typing sequence generics in func_metadata

  bugv1v2
  modelcontextprotocol/python-sdk#3771 · Filter by author chauvuusvn opened on Oct 27, 2026
  3

• 401 and error for a request with no authorization header (for a request with no token) - as per spec no error should be added

  bugv2
  modelcontextprotocol/python-sdk#3769 · Filter by author yedlurisrinu opened on Oct 26, 2026
  2

• Issuers are compared after URL normalisation; partial CIMD client_id URL validation

  bugv2
  modelcontextprotocol/python-sdk#3768 · Filter by author yedlurisrinu opened on Oct 26, 2026
  3

• Client 2026-07-28: missing resultType causes ValidationError despite required complete fallback

  bugspec-2026-07-28v2
  modelcontextprotocol/python-sdk#3767 · Filter by author saigonbaddielover opened on Oct 26, 2026
  1

• 2026 Streamable HTTP rejects whitespace-padded Mcp-Name values

  bugspec-2026-07-28v2
  modelcontextprotocol/python-sdk#3763 · Filter by author DMomplaisir opened on Oct 25, 2026
  4

• Modern Streamable HTTP JSON response mode does not observe client disconnects

  bugv1v2
  modelcontextprotocol/python-sdk#3762 · Filter by author DMomplaisir opened on Oct 25, 2026
  6

• Positional-only handler parameters break tools, prompts and resource templates

  bugv1v2
  modelcontextprotocol/python-sdk#3760 · Filter by author PerryLink opened on Oct 25, 2026
  3

• Progress callbacks run concurrently, out of order, and after call_tool() returns

  bugv2
  modelcontextprotocol/python-sdk#3747 · Filter by author dhruvindave007 opened on Oct 23, 2026
  4

• Examples demonstrate ToolAnnotations only on a tool where they change nothing

  documentation
  modelcontextprotocol/python-sdk#3737 · Filter by author gl1tchdust opened on Oct 21, 2026
  3