Both help(typing.Annotated) and help(typing._AnnotatedAlias) should document the __metadata__ field; based on the comments in #89543 the field was meant to be public but was inadvertently omitted from the PEP and documentation.

Linked PRs

• gh-97797: Mention __metadata__ in docstrings of typing.{_AnnotatedAlias, Annotated} #103405
• [3.11] gh-97797: Mention __metadata__ in docstrings of typing.{_AnnotatedAlias, Annotated} (GH-103405) #103413
• gh-97797: Improve documentation for typing.Annotated #105365
• [3.12] gh-97797: Improve documentation for typing.Annotated (GH-105365) #105448
• [3.11] gh-97797: Improve documentation for typing.Annotated (GH-105365). #105449