- Introduces new concurrent hooks (useId, useTransition/useDeferredValue, useSyncExternalStore, useInsertionEffect) and ReactDOM client APIs (createRoot, hydrateRoot) plus streaming server render APIs.
- Deprecates legacy ReactDOM.render, hydrate, unmountComponentAtNode, renderSubtreeIntoContainer and renderToNodeStream in favor of the new root APIs.
- Breaking changes include automatic batching, stricter StrictMode behavior, consistent useEffect timing, stricter hydration error handling, and require modern JS environment features.
Community impact
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