So their philosophy is to start with zero client-side javascript, even when one is using components from javascript-heavy frameworks like React or Vue. Interactivity is apparently something one has to explicitly opt-in to by adding a client:* directive, rather than it being the default.
The migration guide states, "Astro projects can also be SSG or SSR with page level prerendering," which puts it on par with Nuxt in that regard.
A difference I've noticed regarding server-side features is that Astro allows one to "define and call backend functions with type-safety."[0] which even Nuxt doesnt offer in such a convenient and type-safe manner. I'm pretty happy with what i'm seeing in Astro's docs so far.