If you are on T-Mobile or Verizon and own the HTC One M8, you are about to get the Android 6.0 Marshmallow update on your device.
T-Mobile's software version for their HTC One M8 is 6.20.531.5. Verizon’s update is version, 6.21.605.3.
The update includes some extra features beyond the usual suspects in Marshmallow. These include new volume controls for notifications, audio and alarms, simplified screenshot capture, and more. You will also find Google Now on Tap, updated app permission control, Doze mode, and a few others.
For more details check out the links below:
Source: Verizon, T-Mobile