I've used both in production.
Simply put: if there's a relational database or it's more than just a handful of endpoints, Django REST Framework is the way to go.
FastAPI is like Flask in that it shines where you want it to do very little for you. If you want it to do a lot for "free", the Django-verse is and will continue to be better.
Last of all, I'll add that we refactored away from FastAPI to just use Starlette under the hood, because FastAPI pretty much assumes you want a REST API, and when don't want a REST API, you begin fighting with it.
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