- Breaking changes: deprecated non-JSX component calls, prop mutation warnings, removed autobinding of statics, immediate ref availability after componentDidMount, always async setState, warnings for setState/forceUpdate on unmounted compo...
- New features: ES6 class components, top‑level APIs React.findDOMNode and React.cloneElement, functional setState, callback‑style refs, support for iterators/immutable children, React.addons.createFragment, and JSX target option with ES5/...
- Deprecations: ComponentClass.type, legacy methods on ES6 components (getDOMNode, replaceState, isMounted, setProps, replaceProps), React.addons.classSet, and migration from React.addons.cloneWithProps to React.cloneElement.