Indeed, we use FastAPI in quite a large scale! I would not trade FastAPI for anything else at this point. Before the typing module became ubiquitous there used to be a lot of "magic" frameworks that made heavy use of Python's dynamic nature; both Django and Flask fall within this category: I am not a fan of untyped Python, at all.

There's some gotchas in the way FastAPI works, mostly due to its usage of thread pools and the GIL. I would recommend anyone starting a project to exclusively use asynchronous I/O (SQLAlchemy supports async with asyncpg), as FastAPI is very clearly meant as a pure ASGI framework, despite what they claim.