Given the Python versioning effective convention, it would be strange for the developers to go from 3.9 -> 4.0 because they've run out of digits. Probably better to go to 3.10 to avoid confusion and stay on 3.X while there's no backwards-compatible breaks.

Yup. They eventually decided they might go to 3.10 after 3.9.

From the article above:

> Update: After this post was originally written back in 2014, subsequent discussions on the core python-dev mailing list led to the conclusion that the release after 3.9 will probably just be 3.10. However, a 4.0 will presumably still happen some day, and the premise of this article is expected to hold for that release: it will be held to the same backwards compatibility obligations as a Python 3.X to 3.X+1 update.