In the 3.9 release notes it says "Aliases to Abstract Base Classes in the collections module, like collections.Mapping alias to collections.abc.Mapping, are kept for one last release for backward compatibility. They will be removed from Python 3.10" but the 3.10 release notes don't really mention it. Apparently it's been emitting a DeprecationWarning since Python 3.3 (2012), but still... I like to have things "just work" even if I return to them after 5 or 10 years.
