GitHub Actions: Test on Python 3.14 release candidate 2

[cclauss]

- python-version: ["3.10", "3.11", "3.12", "3.13"]
+ python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]

Python v3.14 -- October 7th

• https://www.python.org/download/pre-releases
• https://www.python.org/downloads/release/python-3140rc2

Call to action
We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.14 during this phase, and publish Python 3.14 wheels on PyPI to be ready for the final release of 3.14.0, and to help other projects do their own testing. Any binary wheels built against Python 3.14.0 release candidates will work with future versions of Python 3.14.

Motivation and Context

Let's ensure things work as expected on the next version of CPython as recommended by the Python Core Team.

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

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

[felixweinberger]

Curious what other maintainers think about adding 3.14 already to our CI @Kludex @dsp-ant @ihrpr

Looks like 3.14 is currently pre-release with release slated for 7 Oct 2025 so relatively soon (https://devguide.python.org/versions/)

[Kludex]

I mean, if you are able to make the pipeline pass, then sure...

[cclauss]

Blocked by

• Add support to python 3.14 squidfunk/mkdocs-material#8419

[Kludex]

We don't really need to build the docs in 3.14.

You can add a marker to not install on that version. python_version < '3.14' should work.

[cclauss]

Sorry. I am out of my depth. uv --all-extras will ignore python_version markers and install everything.

[cclauss]

mkdocs-material v9.6.19 was released, so we can force mkdocs-material[imaging] to use pillow v11.3 instead of v10.

Now the problem is pydantic --> pydantic-core --> pyo3.

Using the alpha release https://pypi.org/project/pydantic/2.12.0a1, we finally get the build to succeed.
However, the Pydantic differences now mean that 7 modelcontextprotocol/python-sdk pytests fail.

[Kludex]

Please put this back.

[cclauss]

https://github.com/astral-sh/uv/releases/tag/0.8.11 Added Python 3.14rc2 and 0.8.12 speeds up zstandard performance.

[Kludex]

You can change the version, but there's no need to remove it.

We actually need to set this version in the pyproject.toml.

[Kludex]

Missing the classifier above.

[cclauss]

?

[Kludex]

This is missing on line 22.

    "Programming Language :: Python :: 3.14",

[cclauss]

I was not going to commit to supporting 3.14 until after we got the tests to pass, but here we go...