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MCP client doesn't not initialize new session when getting 404 session not found

Open david-nominal opened this issue 2 months ago • 0 comments

Initial Checks

  • [x] I confirm that I'm using the latest version of MCP Python SDK
  • [x] I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

Per https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#session-management

When a client receives HTTP 404 in response to a request containing an MCP-Session-Id, it MUST start a new session by sending a new InitializeRequest without a session ID attached.

This is not the case with the python client. It just sends a session terminated error in streamable_http.py

Example Code

Python & MCP Python SDK

mcp: 1.22.0
python: 3.14.0

david-nominal avatar Nov 26 '25 22:11 david-nominal