How does the React Native New Architecture improve performance?

The New Architecture (stable in RN 0.76) addresses the root causes of the old architecture's performance limitations: JSI (JavaScript Interface) — synchronous native calls: the old bridge was always async — calling native code, getting a result, and continuing took at minimum one "tick" (often 1-10ms). With JSI, JavaScript can call native C++ functions synchronously — like calling a regular JavaScript function: // Old (async bridge): NativeModules.Camera.getDeviceOrientation() .then(orientation => { /* delayed */ }) // New (JSI -- synchronous): const orientation = global.getCameraOrientation(); // Instant!. Fabric (new renderer): the rendering pipeline is now implemented in C++ and can run on the JS thread, main thread, or a background thread concurrently. Shadow tree (layout calculation) is also C++. This enables: synchronous layout measurements, concurrent React features (transitions, Suspense in rendering), faster first render (no back-and-forth between JS and native for initial layout). TurboModules: old architecture loaded ALL native modules at startup (even unused ones). TurboModules load lazily — only when first accessed. Plus, they're typed via CodeGen — no runtime type checking. CodeGen: generates type-safe C++ glue code from TypeScript specs. Eliminates entire classes of type mismatch bugs between JS and native. Faster because the type bridge code is generated at build time. React 18 Concurrent Mode: Fabric enables React's Concurrent features — startTransition, useDeferredValue, Suspense for data fetching. The renderer can interrupt non-urgent renders to stay responsive. Real-world impact: faster app startup (TurboModules), smoother animations when combined with Reanimated, better list performance, React 18 features.