This issue is supposed to track when we can start to use the pipe character as union (PEP 604) in typeshed. Support is needed in released versions of:

• mypy (Support PEP 604 - union types as X | Y mypy#9610), mostly works, except (full list of related issues here):
  • Type aliases (3.10 union operator ( | ) doesn't work in subscripts when creating type aliases mypy#10901)
  • False-positive errors when using type[T] (or Type[T]) in a PEP 604 type alias mypy#12392
  • False-positive error when using Callable in a PEP 604 type alias mypy#12393
  • (🐞) False positive "error: Type application has too many types (1 expected)" on tuple when annotated as a type or in a TypeAlias with new union syntax (PEP 604) mypy#11098
  • False-positive error when using Callable in a PEP 604 type alias in a stub file with --python-version=3.9 mypy#14158
• pytype (Add support for PEP 604 (Union |) in stub files google/pytype#924)
• pyright (Implement PEP 604 microsoft/pyright#659)
• pyre
• PyCharm (PY-44974)