Microsoft just pushed Windows 10 Mobile Build 10586.63 to Insiders and after proper testing and feedback from Insiders, this build will be not only pushed to Windows 10 Mobile running normal devices but may also be the upgrade build for windows Phone 8.1 devices.
Now, it seems that Microsoft may be planning to release the Windows 10 version of this build to all normal Windows 10 running devices (non-insider) out there. So, most probably we will see a cumulative update bumping the Windows 10 version to Build 10586.63 on January 12, a day of importance as per a tip we received earlier.
The Build 10586.63 doesn’t bring any noticeable changes but mostly bug fixes and performance improvements. Also, it needs to be kept in mind that minor issues like issue with upgrade servers or a last minute bug may push the release date of this cumulative update further.