The second and final release candidate for Python 3.15 is now available, marking the last opportunity for library maintainers to test their projects before the official release on October 1, 2026. This pre-release phase is crucial for ensuring compatibility and identifying potential issues. Hugo van Kemenade, the release manager, urges maintainers to prepare their third-party projects for Python 3.15 by publishing compatible wheels on PyPI. Testing now helps projects adapt to any removals or changes in Python 3.15, preventing surprises for users upon the final launch. Moreover, maintainers might discover and report bugs in Python itself, contributing to a more robust final release. To test with 3.15 using GitHub Actions, users can add "3.15" and "allow-prereleases: true" to their workflow matrix. It's also an opportune moment to declare support for Python 3.15 by adding the corresponding Trove classifier. For projects with extension modules, releasing binary wheels for 3.15 will assist dependent projects in their testing. There will be no further ABI changes from this point forward in the 3.15 series, with a goal of minimal code alterations. Maintainers are strongly encouraged to start testing their projects with Python 3.15 immediately.