fastapi is very similar to what you’d get from flask with an API spec tool like flast-restx or flask-marshmallow + incubation time to build your own components

fastapi is very similar to what you’d get from flask with an API spec tool like flast-restx or flask-marshmallow + incubation time to build your own components & patterns around it + fastapi is faster. So if you are committed to the component tools you already built with flask add ons, stick to flask unless you need the speedup. Otherwise if the project is new or you’re otherwise uncommitted to your existing component tools, switch to fastapi.