This repository contains example packages for testing the new limited API proposals, along with a test suite. Currently, it uses the reference implementation of PEP 803 found in CPython 3.15.0a2.

This is a work-in-progress, based on the state as of 2026-01-10. Whenever possible, official or semi-official support is used. Elsewhere, hacks are employed, or the packages are as close to the new API as currently possible.

• In packages using the C API, the new limited API is enabled via setting -D_Py_OPAQUE_PYOBJECT as required by Python 3.15.0a2. According to PEP 803, the final implementation should not require this. This is also done on packages that have explicit switches for limited API, since these do not account for PEP 803.
• A minimal fork of meson-python is used, in order to remove the explicit check that blocks disabling GIL while using limited API.
• A preview freethreading-limited-api branch of Cython is used.
• Cython currently fails to actually indicate extension compatibility with GIL disabled. Cython#7399.
• PyO3 does not support PEP 793, PEP 803 or Python 3.15 yet. The test currently builds a limited API extension targeting Python 3.14. PyO3#5610.
• nanobind does not support PEP 793 yet. The test package uses regular limited API or freethreading API currently. nanobind#1187.
• None of the build systems implement the new wheel tags found in PEP 803. As such, tests are not currently looking at wheel tags.