Windows 10 Mobile Build 10586.63 is now available for Insider

Microsoft started rolling out of Windows 10 Mobile Technical preview build 10586.63 to the insiders in the fast ring. Usually this update is a just a cumulative update . That means nothing new in this update.Only bug fixes and performance improvements.

Microsoft stopped providing changelogs for their updates, but a friendly Microsoftie on Reddit did provide the following list of improvements:

General reliability improvements
battery and performance improvements
Typing on Polish keyboard in Outlook Mail
Turn by turn directions over Bluetooth in car
Battery usage with Iris Recognition
Reliability of quick actions settings page
MS Band use with Cortana