See https://bugs.python.org/issue44477. PEP 509 is no longer used in CPython, we should repeal it to save space on all dictionaries using ma_version_tag.

I volunteer to write the PEP to repeal PEP 509.

Things the PEP will need to cover:

• Deprecation cycle
• Impact on external libraries (e.g. Cython).
• Whether we need alternatives for current use cases.

Some preliminary research tells me that Cython does use it for cached global lookups.
We may need to offer a (private, unstable) alternative to looking up globals.

CC @vstinner