Animation API: As mentioned above, there is a new API for animating components. See the animation documentation to learn more.
Text decoration: The Text component supports various CSS-like decoration props: textDecorationColor, textDecorationLine, and textDecorationStyle. See UIExplorer and the documentation for the supported values.
Opaque nav bar:NavigatorIOS has a new prop called translucent. Set it to false to turn the nav bar opaque.
Scroll view composition:ListView has a new prop called renderScrollComponent. Set it to a function that takes props and returns a scroll view element. This allows you to return custom scroll views.
Image load events: The Image component supports three new events for downloaded images: onLoadStart, onLoadProgress, and onLoadError
System font: There is a special font family called "System" that tells Text components to use the system font. Apps on iOS 9 will use San Francisco instead of Helvetica Neue. In addition, the system font on iOS is configured with several typographical options like the widths of digits and vertical positioning of colons that the Apple font team has chosen.
iOS
Fewer UIViews: Improved rendering performance by eliding UIViews for shadow views that solely affect layout. 02db374
RCTResponseErrorBlock: Authors of native modules now can use RCTResponseErrorBlock(NSError *) instead of RCTResponseSenderBlock(id) to pass errors back to JavaScript.
NSSet coercion: Native module methods now can have parameter of type NSSet. RCTConvert will automatically convert JavaScript arrays to NSSet objects.
Packager
Custom transformers: You can pass --transform /a/path/to/a/transformer.js to the packager to customize how it transforms your app's JavaScript source code.
Faster Babel: The packager uses a faster version of babel-core for a 40% improvement in transformation 7d184ad
io.js and V8: io.js includes a modern version of V8, which improves the packager's performance by around 5-10%
Bug Fixes
Improved scene and focus management in Navigator 7963adde3e6098