The RSC rendering pipeline

Three pieces arrive for different reasons

• HTML gives the browser a useful initial representation.
• The RSC payload describes rendered Server Component output and references to Client Components.
• Client JavaScript provides the implementation needed to hydrate and run interactive components.

The RSC payload is not HTML

React uses a framework-managed serialized representation for Server Component output. It lets React reconcile the server-rendered tree and understand where Client Components belong.

The important consequence is architectural: a Server Component can contribute UI without its implementation becoming ordinary client-side application code.

From component tree to interactive page

Hydration is where interaction wakes up

Server-rendered HTML can be visible before every interactive component is ready. Hydration attaches React's client behaviour to the relevant markup.

This is one reason client bundle size still matters in a server-first application. Unnecessary client boundaries mean more code to download, parse, execute, and hydrate.