Definition
Server-Side RenderingSSR
Server-side rendering (SSR) generates a page's HTML on the server so the content is present in the initial response, before any JavaScript runs. It's how you make sure AI crawlers, which typically don't execute JavaScript, can actually read your content.
Static generation (SSG) achieves the same for content that doesn't change per request. Either way, the goal is: critical content in the raw HTML.
Is server-side rendering necessary for AEO?
Not strictly SSR specifically, but your critical content must be in the raw HTML. SSR or static generation are the reliable ways to guarantee that for AI crawlers that don't run JavaScript.