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Title: [v1.x] build: restrict httpx to <1.0.0 by maxisbey · Pull Request #2559 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: [v1.x] build: restrict httpx to <1.0.0 by maxisbey · Pull Request #2559 · modelcontextprotocol/python-sdk

X Title: [v1.x] build: restrict httpx to <1.0.0 by maxisbey · Pull Request #2559 · modelcontextprotocol/python-sdk

Description: Backport of #2345 to the v1.x release branch. Closes #2543. Motivation and Context httpx publishes 1.0.dev1/1.0.dev2/1.0.dev3 pre-releases on PyPI. These are a ground-up rewrite with an incompatible public API — no AsyncClient, Auth, Timeout, BasicAuth, codes, or the TransportError/StreamError exception hierarchy. The current v1.x constraint is unbounded (httpx>=0.27.1), so when a downstream package is installed with pip install --pre (common for alpha/beta libraries built on mcp), pip resolves httpx 1.0.dev3 and import mcp fails immediately: File ".../httpx_sse/_exceptions.py", line 4, in class SSEError(httpx.TransportError): ^^^^^^^^^^^^^^^^^^^^ AttributeError: module 'httpx' has no attribute 'TransportError' This was already fixed on main in #2345 but never backported, so all published 1.x releases (including 1.27.0) are affected. How Has This Been Tested? Reproduced in a fresh venv: python -m venv /tmp/repro && /tmp/repro/bin/pip install --pre 'mcp==1.27.0' /tmp/repro/bin/python -c 'import mcp' # AttributeError: module 'httpx' has no attribute 'TransportError' Confirmed that constraining to httpx<1.0 (resolves 0.28.1) restores all of import mcp, stdio_client, sse_client, and streamablehttp_client. Breaking Changes None. httpx 0.28.1 remains the latest stable; this only excludes the incompatible 1.0 dev pre-releases. Types of changes Bug fix (non-breaking change which fixes an issue) Checklist I have read the MCP Documentation My code follows the repository's style guidelines New and existing tests pass locally I have added appropriate error handling I have added or updated documentation as needed Additional context Re the alternatives raised in #2543: <2.0 wouldn't help — httpx 1.x is API-incompatible by design, not just pre-release churn. Not adding a speculative httpx-sse<1.0 cap; no such release exists and we'd rather not pre-emptively constrain a dep that hasn't broken. AI Disclaimer

Open Graph Description: Backport of #2345 to the v1.x release branch. Closes #2543. Motivation and Context httpx publishes 1.0.dev1/1.0.dev2/1.0.dev3 pre-releases on PyPI. These are a ground-up rewrite with an incompatibl...

X Description: Backport of #2345 to the v1.x release branch. Closes #2543. Motivation and Context httpx publishes 1.0.dev1/1.0.dev2/1.0.dev3 pre-releases on PyPI. These are a ground-up rewrite with an incompatibl...

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og:image:altBackport of #2345 to the v1.x release branch. Closes #2543. Motivation and Context httpx publishes 1.0.dev1/1.0.dev2/1.0.dev3 pre-releases on PyPI. These are a ground-up rewrite with an incompatibl...
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30ccd99 [v1.x] build: restrict httpx to <1.0.0 maxisbey May 8, 2026 https://github.com/modelcontextprotocol/python-sdk/pull/2559/commits/30ccd99febc0d53a697827ea8a569f74f3c076e0
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