No, not like Gatsby. Blitz can have client-rendered, SSR, and static all in the same app, on a page-by-page basis (same as Next.js)
The special sauce is the Blitz queries & mutations. You import them directly into your components like a local function, but at build time Blitz swaps in an RPC layer that runs the query/mutation on the server.
So the DX is “no API”, but it does use an API behind the scenes.