Help test Python 3.15!

Table of Contents

Calling all Python library maintainers! 🐍

The second and final Python 3.15 release candidate is out! 🎉

It’s your last chance to join the cool testers’ club and say that YOU helped test 3.15 before the big day on 1st October! 😎

PEP 790 defines the release schedule for Python 3.15.0:

The first release candidate came out on 4th August 2026
The second release candidate came out on 1st September 2026
And the full release is set for 1st October 2026

In his announcement, Hugo van Kemenade (👋 hi, that’s me!), release manager for Python 3.14 and 3.15, gave a call to action:

We strongly encourage maintainers of third-party Python projects to prepare their projects for 3.15 during this phase, and publish Python 3.15 wheels on PyPI to be ready for the final release of 3.15.0, and to help other projects do their own testing. Any binary wheels built against Python 3.15.0 release candidates will work with future versions of Python 3.15. As always, report any issues to the Python bug tracker.

Test with 3.15 #

It’s now time for us library maintainers to start testing our projects with 3.15. There’s two big benefits:

There have been removals and changes in Python 3.15. Testing now helps us make our code compatible and avoid any big surprises (for us and our users) at the big launch in October.
We might find bugs in Python itself! Reporting those will help get them fixed and help everyone.

How #

To test the latest alpha, beta or release candidate on GitHub Actions with actions/setup-python, add 3.15 and allow-prereleases: true to your workflow matrix.

For example:

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        python-version: ["3.11", "3.12", "3.13", "3.14", "3.15"]

    steps:
      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1

      - name: Set up Python ${{ matrix.python-version }}
        uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
        with:
          python-version: ${{ matrix.python-version }}
          allow-prereleases: true

(We can instead use 3.15-dev and omit allow-prereleases: true, but I find the above a bit neater, and when 3.15.0 final is released in October, it will continue testing with full release versions.)

When to support 3.15? #

Now is also a good time to declare support and add the Programming Language :: Python :: 3.15 Trove classifier. Many projects already have!

Especially if you have extension modules and other projects depend on yours, a release with binary wheels will help them test and prepare.

ABI breaks? #

From the announcement:

There will be no ABI changes from this point forward in the 3.15 series, and the goal is that there will be as few code changes as possible.

Let’s start testing 3.15 now! 🚀

Test with 3.15 #

How #

When to support 3.15? #

ABI breaks? #

See also #