When will PyO3 support Python 3.14?

[Clayblockunova]

I'm trying to install agentlightning (a python lib), and rust says:
the configured Python interpreter version (3.14) is newer than PyO3's maximum supported version (3.13)
When will PyO3 support Python 3.14?

[davidhewitt]

PyO3 has supported in-development builds of 3.14 for some time, we released 0.27 with full support for 3.14 final.

I suspect agentlightning needs to update a dependency.

[ericgitangu]

Building on @davidhewitt's reply — agentlightning itself is pure Python (microsoft/agent-lightning), so the PyO3 floor almost certainly comes from a transitive Rust extension being built from sdist on 3.14 because no wheel exists yet. The two usual suspects in that dependency tree are tokenizers and safetensors, both of which ship pyo3-backed wheels but lag a few weeks behind a new CPython release.

To pin down which crate is forcing the build:

pip install --no-binary :all: -v agentlightning 2>&1 | grep -E "Building|maturin|pyo3"

The first failing build line names the package. From there:

pip download <that-package> --no-binary :all: --no-deps
tar -xzf <that-package>-*.tar.gz
grep -r '^pyo3' <that-package>-*/Cargo.toml

If the version is pyo3 = "0.22" or older, it genuinely doesn't know about 3.14 and you're waiting on the upstream maintainer to bump. Workarounds in order of preference:

1. Use Python 3.13 in a separate venv until the package cuts a 3.14 wheel (PyO3 historically gets full support in by the X.0 release matching CPython's stable cut, and 0.27 hit that mark for 3.14).
2. If you control the build, fork and bump the pyo3 dep — most extensions need only a minor version bump from 0.22/0.23 to 0.27+.
3. Pre-built wheels appear on PyPI within a few weeks of CPython final; the PyO3 migration guide covers the breaking changes between minor versions if you do fork.

The cargo tree -p pyo3 output from a clone of the offending crate is the fastest way to confirm which version it's actually pulling.