FastAPI vs Flask

FastAPI is a younger framework (2018) built on Starlette and Pydantic; Flask is the long-standing minimal WSGI framework (2010). FastAPI is the default for new async Python APIs with type hints, while Flask remains the go-to for simple, no-magic services and teaching. Pick FastAPI when you want OpenAPI docs and async for free; pick Flask when you want a small dependency footprint and a decade of ecosystem.