Environment marker for free-threading

Packaging
21

It doesn’t, all it says is (docs link):

Return True if the GIL is enabled and False if it is disabled.

Added in version 3.13.

22

Yeah, go ahead and copy whatever sys._is_interned has used to get its note. Should be a trivial PR.

23

I’ve left some comments on the PR about the current proposed sys.abi_features API: