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Image content blocks >99 bytes fail with "illegal base64 at byte 0"

Status: Open.

#3123 In modelcontextprotocol/python-sdk;

· PeeperFrog opened on Jul 18, 2026

Server._handle_message can loop forever re-logging warnings when a log handler itself emits a warning (v1.x)

Status: Open.

#3122 In modelcontextprotocol/python-sdk;

· fas89 opened on Jul 17, 2026

Recommended deployment pattern for FastMCP on AWS Lambda using Mangum

questionFurther information is requestedFurther information is requested

Status: Open.

#3121 In modelcontextprotocol/python-sdk;

· shoaib1207k opened on Jul 17, 2026

RequireAuthMiddleware omits RFC 6750 scope in WWW-Authenticate on 401/403

Status: Open.

#3103 In modelcontextprotocol/python-sdk;

· velias opened on Jul 16, 2026

Streamable HTTP server never returns the spec-mandated 405 for GET requests it won't serve as SSE (406/400 instead) — breaks client SSE-probe fallback

Status: Open.

#3102 In modelcontextprotocol/python-sdk;

· fgranata opened on Jul 16, 2026

Generated output schema uses Pydantic's validation shape while structured output uses its serialization shape

Status: Open.

#3100 In modelcontextprotocol/python-sdk;

· destire-mio opened on Jul 16, 2026

Field alias is published in the tool schema but forwarded as an invalid Python keyword

Status: Open.

#3099 In modelcontextprotocol/python-sdk;

· destire-mio opened on Jul 16, 2026

streamable_http: HTTP status errors (401/403/5xx) on tools/list, tools/call never reach the caller — indistinguishable from a timeout

Status: Open.

#3091 In modelcontextprotocol/python-sdk;

· afterrburn opened on Jul 13, 2026

Heavy sync init work (e.g. local ML models) starves stdio initialize/tool calls even with threadpool offload -- Windows GIL contention

Status: Open.

#3089 In modelcontextprotocol/python-sdk;

· scotthibbs opened on Jul 12, 2026

FastMCP tool argument models silently ignore unknown/misspelled arguments (extra=ignore default)

v2Ideas, requests and plans for v2 of the SDK which will incorporate major changes and fixesIdeas, requests and plans for v2 of the SDK which will incorporate major changes and fixes

Status: Open.

#3067 In modelcontextprotocol/python-sdk;

· ramonahl opened on Jul 6, 2026

[v2] RFC 9728 PRM URLs and resource matching drop query components

v2Ideas, requests and plans for v2 of the SDK which will incorporate major changes and fixesIdeas, requests and plans for v2 of the SDK which will incorporate major changes and fixes

Status: Open.

#3065 In modelcontextprotocol/python-sdk;

· mayankbohradev opened on Jul 6, 2026

streamable HTTP (stateful): concurrent requests with duplicate JSON-RPC ids cross-wire responses — one request receives another's payload, the other hangs

Status: Open.

#3060 In modelcontextprotocol/python-sdk;

· scottmsilver opened on Jul 3, 2026