T-Mobile has started the rollout of the latest major version of Android - Marshmallow, which was released in October last year - to the HTC One M9. This makes it the third carrier, following Sprint and Verizon, to bring Marshmallow to the device.
The new update is arriving in two parts, with an update of about 97 MB, which prepares your phone for the upgrade and a second, larger update, which comes in at 1.32 GB, which will upgrade your device to the newest version.
Exact changes that are implemented in the update are not available, though, as both T-Mobile and HTC decided not to post detailed change logs - but changes that are mentioned are the new doze mode, which aims to conserve your battery life by restricting access to network and CPU-intensive services for apps, and the 'do not disturb' mode which silences your devices and disables vibration.
Also mentioned are app permissions, which means that apps will now ask for permissions when they need it (compared to when you install them); an updated version of verified boot; flex storage, which allows you to use external storage as internal storage; and Google Now on Tap.
More information about the update and the steps and requirements to install it can be found on the support page on the T-Mobile website.
Source: International Business Times