3.14 regression: `Union[int, str] is Union[int, str]` does not hold

[hroncok]

Bug report

Bug description:

Python 3.13.2

>>> from typing import Union
>>> Union[int, str] is Union[int, str]
True

Python 3.14.0a6

>>> from typing import Union
>>> Union[int, str] is Union[int, str]
False

Is this change desired, is it documented? This breaks tests in https://github.com/python-attrs/cattrs/blob/d8f17b7e7e57006171027df4d647a6fe068b623e/tests/test_disambiguators.py#L211

assert fn({"op": 0, "t": "MESSAGE_CREATE"}) is Union[F, G]

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-131933: Document UnionType/Union merger in What's New #131941

[hugovk]

Bisects to dc6d66f, PR #105511, issue #105499: "Merge typing.Union and types.UnionType".

[picnixz]

cc @JelleZijlstra