It's been a stable (and documented) behavior of the Python standard library for almost a decade now. It's possible it may change--nothing is ever set in stone--but that would be a large change in Python that would come with plenty of warning and time for adjustment.
Well, in my early days programming python I made a lot(!!) of code assuming non-concurrent execution, but some of that code will break in the future with GIL removal. Hopefully the Python devs keep these important changes as opt-ins.
And then one day, Astral creates a new Python implementation in Rust or something that is way faster and all the rage, but does this particular thing different than CPython. Whoops, you can’t use that runtime, because you now have cursed parts in your codebase that produce nondeterministic behaviour you can’t really find a reason for.