As discussed in dpo-38423 implemented in gh-121277 and documented in devguide:
You can now use next in documentation version directives to target the upcoming release of the current branch (main for now, backports will follow):
.. versionadded:: next
.. versionchanged:: next
.. versionremoved:: next
.. deprecated:: next
.. deprecated-removed:: next 3.20
(here the second version, "removed in", can't be `next`)
When a release is cut, the next will be replaced with the release’s number.
Before the backports are in place, you can use this grep to check if next will work in your branch:
grep expand_version_arg Doc/tools/extensions/pyspecific.py