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

Headline: React Compiler — formerly React Forget — shipped stable with React 19 and automatically memoizes components, hooks, and callbacks by analyzing data flow at build time. No dependency arrays to write; the compiler infers them. Here is what it handles, when it opts out, and whether you should delete your useMemo calls. Key takeaways React Compiler inserts useMemo , useCallback , and React.memo automatically at build time — no dependency arrays to maintain. Enable it in Next.js 15/16 with experimental.reactCompiler: true in next.config.ts . The compiler is conservative: if it cannot prove memoization is safe, it emits the component unchanged. "use no memo" is the escape hatch for functions the compiler should not touch. Run npx react-compiler-healthcheck@latest before enabling to see coverage and violations. What does React Compiler actually do? React Compiler transforms component and hook code at build time to insert memoization automatically. Instead of useMemo(() => expensiveCalc(a, b), [a, b]) , the compiler analyzes data flow, determines which values are stable across renders, and emits equivalent memoized code. The compiled output uses React's memo infrastructure at runtime. The compiler is babel-plugin-react-compiler — it works with any Babel-based build pipeline. How do I enable it in Next.js? // next.config.ts const nextConfig = { experimental : { reactCompiler : true , }, }; export default nextConfig ; Before enabling, run the healthcheck: npx react-compiler-healthcheck@latest The healthcheck reports optimizable component count, files with violations, and blocking patterns. Fix violations first for more coverage on day one. What does the compiler memoize? Components — equivalent to React.memo ; re-renders only when props change. Values — equivalent to useMemo ; computed results, derived arrays, objects. Callbacks — equivalent to useCallback : event handlers, functions passed as props. Dependencies are inferred from escape analysis — n