Been there, buddy. We used Flask for our MVP and scaling was fine, but you need to throw in some work like adding a WSGI server like Gunicorn later. No silver bullet! Just get something out and see users' reactions.

Look, are you trying to run Google here? For an MVP, anything works as long as you ship it quick. But, in the past, we stayed away from shiny new toys until they're robust. Remember, early tech can be risky.

I'm a fan of FastAPI for MVPs but honestly, it comes down to what you're comfortable with. Use what fits your stack and your team's expertise. It doesn't hurt that FastAPI is super fast and has async support.

I dunno, man. If you're focusing on APIs and worried about scaling later, have you considered the team size you'll have in future? Might matter if you pick something that fewer devs know well.

Flask is great if you like to keep things minimal and Pythonic. You're not traded with boilerplate and can grow from a microservice to something more substantial without hassle. You need some discipline for organizing bigger projects, though.

Can someone explain why scalability is different in these frameworks? Like, are they easier to scale because of how they're built, or is it about available tools and community support? Trying to wrap my head around it.

Express.js is a tried and true option, especially if you're already familiar with JS/Node. It's lightweight and flexible enough for a quick MVP. Lots of middleware options too!

FastAPI all the way for quick prototyping. It's built on top of Starlette, so it's super fast and async ready, which makes it excellent for scaling later. Plus, the auto-generation of Swagger docs is a big plus for me.