New Next.js Guide Focuses on App Router

The App Router was introduced as a beta feature in Next.js 13 on October 26, 2022, and became stable with version 13.4 in May 2023. This represented a fundamental paradigm shift, moving from the client-centric "Pages Router" to a server-first architecture built on React Server Components (RSC). This new model was created to address performance bottlenecks and improve developer experience by leveraging modern React 18 features. Unlike the previous Pages Router, where components are client-side by default, the App Router renders components on the server first, drastically reducing the amount of JavaScript sent to the browser. React Server Components (RSCs) are the core technology, allowing developers to write UI that runs exclusively on the server. This enables direct access to backend resources like databases from within the component, without needing to build a separate API layer, and prevents sensitive logic from being exposed to the client. Data fetching is now simplified, moving away from older methods like `getStaticProps` or `getServerSideProps`. Developers can use native `async/await` directly within server components to fetch data, while Next.js automatically handles request deduplication and provides flexible caching options. User experience is enhanced through built-in support for streaming and suspense. The server can send UI components to the client as they are rendered, allowing users to see parts of a page immediately while the rest of the data loads in the background, which improves perceived performance. The App Router also introduced a more powerful file-based routing system with special files like `layout.tsx` for creating nested UIs that persist across navigation, and `loading.tsx` which automatically shows a fallback UI while a route segment loads.