Bug report

I think #105499 was a mistake. types.UnionType was intentionally named so to avoid confusion with typing.Union (see #88895). types.UnionType should not be subscriptable because it is not generic type (and if it was a generic type, subscription would have different semantic than for typing.Union). types.UnionType corresponds to typing._UnionGenericAlias, not typing.Union (see #89581 (comment)).

So we should restore typing.Union, make typing._UnionGenericAlias an alias of types.UnionType, and make types.UnionType non-subscriptable again.

Linked PRs

• gh-137065: Unmerge types.UnionType and typing.Union #137069