Newly released to the Fast Ring Insiders
- Windows Update performance and reliability improvements
- Improvements in migration of data profiles and messaging settings when upgraded from Windows Phone 8.1.
- SensorCore API’s are now upgraded correctly from Windows Phone 8.1; allowing applications, including many fitness applications, to correctly access movement data.
- SD card detection has been improved on boot and after insertion; File Explorer now handles the removal of an SD card when the default for apps or photos are set to SD.
- Improvements in the Edge browser, including PDF rendering.
- Bluetooth improvements when re-connecting to already paired devices and cars; turn by turn directions, and when using Cortana with the Microsoft Band.
- Improvements in Settings when downloading Maps or changing Quick Settings.
- Reinstalling Groove Music from the Windows Store no longer causes DRM music playback issues. Groove Music local song collections are now more quickly imported within the application
- Device power improvements after listening to music, after missed phone calls when iris detection is disabled, and when downloading updates.
- In app purchases now work correctly when cellular data is disabled.
- Improvements to the reliability of Kids Corner.
Source: Windows Blog