How React Server Components Use Streaming and Client Boundaries to Speed Up Apps

React Server Components (RSC) allow components to run entirely on the server, sending serialized UI instructions to the browser instead of full HTML, which reduces client-side bundle size and speeds up first paint. Rather than waiting for the entire component tree to render, the server streams serialized chunks of component data to the client as soon as each piece is ready. The client runtime incrementally parses these chunks and merges them into the UI, enabling progressive rendering. When the server encounters a client component, it inserts a placeholder in the stream; the client then fetches the required JavaScript bundle and hydrates that component in place. This separation of server and client logic, stitched together through a custom serialization format, addresses common issues like hydration mismatches and bloated client bundles seen in traditional server-side rendering.