Mostly the better documentation (last I checked FastAPI docs felt more like a series of blog posts than actual docs, but maybe that's improved). I also preferred the community-driven approach of Litestar as opposed to FastAPI's BDFL-type development structure.

I think there were also some technical details I liked better about Litestar where it was more explicit about things while FastAPI was more "opaque magic happening in the background", but to be honest I don't remember all of those.

We chose Litestar over FastAPI mostly because they seemed very similar, but Litestar had a more distributed governance; i.e. a larger bus factor.

We are jealous of some FastAPI features though, so it's possible we could migrate, as Litestar's mapping between domain models, database models and API models isn't as flexible as we'd like.