Cannot start uvicorn with newly generated app

[svanschalkwyk]

Python 3.9 clean install
Ubuntu 21.04
Paths redacted for clarity
Uvicorn works for a simple app

Traceback (most recent call last):
  File ".../main.py", line 2, in <module>
    from app.api import app
  File ".../app/api.py", line 15, in <module>
    from app.models import (
  File ".../app/models.py", line 44, in <module>
    class RecordDataResponse(BaseModel):
  File ".../.venv/lib/python3.9/site-packages/pydantic/main.py", line 212, in __new__
    fields[ann_name] = Field.infer(
  File ".../.venv/lib/python3.9/site-packages/pydantic/fields.py", line 145, in infer
    return cls(
  File ".../.venv/lib/python3.9/site-packages/pydantic/fields.py", line 122, in __init__
    self.prepare()
  File ".../.venv/lib/python3.9/site-packages/pydantic/fields.py", line 187, in prepare
    self._populate_sub_fields()
  File ".../.venv/lib/python3.9/site-packages/pydantic/fields.py", line 243, in _populate_sub_fields
    self.type_ = self.type_.__args__[0]  # type: ignore
  File "/usr/lib/python3.9/typing.py", line 706, in __getattr__
    raise AttributeError(attr)
AttributeError: __args__