Python 3.9 just appeared on the horizon.
It should be supported in future versions.

Add Python 3.9 to:

• dependencies
• GitHub Action (as of now GitHub does not feature Python 3.9)
• Recursive models throw an exception with Python 3.9.0 pydantic/pydantic#1985
• py3.9 pydantic.errors.ConfigError: duplicate validator function pydantic/pydantic#2009