New features include the return of double tap to wake to modern Windows 10 Mobile devices like the Lumia 950 and Lumia 950 XL and the fix for recurring Wi-Fi disconnections. Here is the full changelog posted by Microsoft :

Besides a new Fast Ring update today owners of the Microsoft Lumia 950 and Lumia 950 XL should check for something else. New firmware with the build 01078.00053.16236.35xxx is now live for many devices in different regions regardless of Insider-status. However, this will be a rolling update (our AT&T Lumia 950 is not seeing it) so not all available devices will receive it today.

Wi-Fi connectivity improvements, including fixes for Wi-Fi connection dropping randomly and Wi-Fi scan occasionally not returning any results.

Support for double tap to wake enabled.

Bluetooth connectivity improvements.

Stability and reliability improvements.

Camera improvements, including improved image and video quality, improved Auto-focus and fix for a problem that was causing slow motion capture to skip frames for some users.

Cellular connectivity improvements, including fix for a problem that caused occasional network loss for some users.

Audio quality improvements, including fix for a problem that caused voice call audio to get scrambled for some users.

Microsoft cautions:

The availability of the update may depend on your phone model, region or network service provider. Starting today, the update should become available for the first batch of phones and the remaining ones are expected to receive the update gradually.

To get the update go to Settings > Update & security > Phone update > Check for updates. If eligible you will see MICROSOFTMDG update waiting. We already have numerous reports of the firmware being live now for the phones as mentioned earlier.

Assuming your phone's region and model number are supported Insiders (Fast, Slow, Release Preview) and non-Insiders should be eligible for the firmware. There is no need to reset or rollback your phone using the Windows Device Recovery Tool. For those on AT&T or phones that do not yet have the update, it should come out over the next few weeks. AT&T's turn-around time is usually about 10 days, though it can vary.

Thanks, Alessandro and Jorn, for the tips