I think FastAPI's one major design difference is its dependency injection mechanism. Django is designed to do things differently, with services provided through an app- or project-global collection of middlewares (although I haven't used it in a while, maybe something had changed since then) and while there are DI solutions for Django they don't feel "native" to me - not the way FastAPI does it. Either way works, of course - it's probably merely a matter of the preferred mental model.