We need to still maybe add a better way to document this? @vstinner Where would you like for the documentation for this change to live?

We need to still maybe add a better way to document this? @vstinner Where would you like for the documentation for this change to live?

Can you at least backport the NEWS entry?

We need to still maybe add a better way to document this? @vstinner Where would you like for the documentation for this change to live?

One option is to add a "Notable changes in Python 3.8.3" section since the change is backward incompatible. Something like:
https://docs.python.org/dev/whatsnew/3.8.html#notable-changes-in-python-3-8-1

But it's up to you to decide if it's worth it or not. The 3.9 change is documented in What's New in Python 3.9, in the "Porting to Python 3.9" section:
https://docs.python.org/dev/whatsnew/3.9.html#changes-in-the-python-api

Oh, seems like @isidentical used the new | operator on dict:

======================================================================
ERROR: test_ensure_flags_dont_clash (test.test_future.FutureTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/python/cpython/Lib/test/test_future.py", line 88, in test_ensure_flags_dont_clash
    flags |= {
TypeError: unsupported operand type(s) for |=: 'dict' and 'dict'
----------------------------------------------------------------------

I will update the PR soon to solve this and with @vstinner suggestions

@pablogsal: Status check is done, and it's a success ✅ .