I believe some of these improvements were part of the same work to eventually remove the GIL (global interpreter lock), albeit not tied to it. However, the final decision on removing the GIL hasn't been made.

Sam Gross has been working on a branch that removes the GIL and has a few other performance improvements. More details are here on the python mailing list: https://mail.python.org/archives/list/python-dev@python.org/...

There's a link to his design overview document in the thread.

There was an experimental branch where someone reimplemented Python 3.9 sans the Gil and managed to maintain performance parity with the Gil’ed version. It’s likely this performance uplift is through the various optimisations that PR implemented.