Currently, unions created throughtyping.Union[A, B] and through thePEP-604 syntaxA | B are at runtime instances of completely different types, and they differ in exactly what elements they accept. This is confusing and makes it harder for users to detect unions at runtime.

I propose to proceed in two steps:

1. Maketyping.Union an alias fortypes.UnionType and make it sotypes.UnionType[A, B] works, accepting the same typesUnion accepts now.
2. Loosen the rules for what the| operator accepts to accept more types that are commonly used in unions.

Linked PRs

• gh-105499: Merge typing.Union and types.UnionType #105511
• gh-105499: Defer "import warnings" in typing #132061