• support generic models with discriminated union, #3551 by @PrettyWood
• keep old behaviour of json() by default, #3542 by @PrettyWood
• Removed typing-only __root__ attribute from BaseModel, #3540 by @layday
• Build Python 3.10 wheels, #3539 by @mbachry
• Fix display of extra fields with model __repr__, #3234 by @cocolman
• models copied via Config.copy_on_model_validation always have all fields, #3201 by @PrettyWood
• nested ORM from nested dictionaries, #3182 by @PrettyWood
• fix link to discriminated union section by @PrettyWood

Full Changelog: https://github.com/samuelcolvin/pydantic/compare/v1.9.0a1...v1.9.0a2

Discussion and feedback: #3538