React Compiler in 2026: What It Actually Memoizes (And What It Doesn't)

React 19 introduces the React Compiler, formerly React Forget, which automatically inserts useMemo, useCallback, and React.memo by analyzing data flow at build time, eliminating manual dependency arrays. It remains conservative, leaving components unchanged if safety is unproven. Additionally, React Server Component boundaries rely on a single serializer to encode props. If the serializer lacks a specific branch for a value, the build fails during prerender, creating potential traps for developers during the serialization process.