Support for free-threaded Python 3.14

[aureliobarbosa]

Many python packages are starting to enable the free-threaded python versions. It would be nice if this could be considered for this package since there is at least one downstream package (timezonefinder) working on this direction jannikmi/timezonefinder#364.

I did some investigation by installing h3-py alongside pytest-run-parallel and found no issue (while working on this one must set the environment variable PYTHON_GIL=0).

Although this result only indicates that maybe this library can be deployed to thread-free python, it is also possible that tests are not sufficiently extensive and didn't touch cases where it would fail in a thread-free python run.

[aureliobarbosa]

This package is currently providing wheels for free thread python 3.14 (windows, macosx, an manylinux) but when imported from 3.14t it emits the following warning:

Python 3.14.6 free-threading build (main, Jun 11 2026, 04:03:14) [Clang 22.1.3 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import h3
<frozen importlib._bootstrap>:491: RuntimeWarning: The global interpreter lock (GIL) has been enabled to load module 'h3._cy.cells', which has not declared that it can run safely without the GIL. To override this behavior and keep the GIL disabled (at your own risk), run with PYTHON_GIL=0 or -Xgil=0.
>>> h3.__version__
'4.5.0'
>>> import sys; sys._is_gil_enabled()
True

The major problem here is that it is re-enabling the GIL, and will block any multi thread code using h3, even if h3 is called in a single thread. As the warning indicates, there is a workaround, but it is an additional problem for upstream projects willing to support free thread (e.g., timezonefinder).

The creation of the wheel occurs due to a catch all flag on the CI job make_wheels from flows/wheels.yml.

h3-py/.github/workflows/wheels.yml

Line 64 in 2883945

build: 'cp*-macosx_arm64'

And I imagine that this is an unintended consequence of Free-threaded Python being officially supported. Is this the case?

It is possible to either disable the this wheel by setting CIBW_SKIP on CI or to annotate the cython code as supporting free threading. I did test the later approach and it looks that it works. If the maintainers are OK with this approach I can submit a PR.

@jongbinjung
@ajfriend
Regards