Sourced from fastapi's releases.

0.119.0

FastAPI now (temporarily) supports both Pydantic v2 models and pydantic.v1 models at the same time in the same app, to make it easier for any FastAPI apps still using Pydantic v1 to gradually but quickly migrate to Pydantic v2.

from fastapi import FastAPI
from pydantic import BaseModel as BaseModelV2
from pydantic.v1 import BaseModel
class Item(BaseModel):

name: str

description: str | None = None
class ItemV2(BaseModelV2):

title: str

summary: str | None = None
app = FastAPI()
@​app.post("/items/", response_model=ItemV2)

def create_item(item: Item):

return {"title": item.name, "summary": item.description}

Adding this feature was a big effort with the main objective of making it easier for the few applications still stuck in Pydantic v1 to migrate to Pydantic v2.

And with this, support for Pydantic v1 is now deprecated and will be removed from FastAPI in a future version soon.

Note: have in mind that the Pydantic team already stopped supporting Pydantic v1 for recent versions of Python, starting with Python 3.14.

You can read in the docs more about how to Migrate from Pydantic v1 to Pydantic v2.

Features

• ✨ Add support for from pydantic.v1 import BaseModel, mixed Pydantic v1 and v2 models in the same app. PR #14168 by @​tiangolo.

0.118.3

Upgrades

• ⬆️ Add support for Python 3.14. PR #14165 by @​svlandeg.

0.118.2

Fixes

• 🐛 Fix tagged discriminated union not recognized as body field. PR #12942 by @​frankie567.

Internal

... (truncated)

• 2e721e1 🔖 Release version 0.119.0
• fc7a068 📝 Update release notes
• 3a3879b 📝 Update release notes
• d34918a ✨ Add support for from pydantic.v1 import BaseModel, mixed Pydantic v1 and ...
• 352dbef 🔖 Release version 0.118.3
• 96e7d6e 📝 Update release notes
• 3611c3f ⬆️ Add support for Python 3.14 (#14165)
• 942fce3 🔖 Release version 0.118.2
• 13b067c 📝 Update release notes
• 185cecd 🐛 Fix tagged discriminated union not recognized as body field (#12942)
• Additional commits viewable in compare view

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