Check the official Android 4.4.4 change log:
So, if you own one of the Google Play Editions of the HTC One, the Android 4.4.4 update is already available over-the-air and is probably waiting for you.
The new update comes less than a month after the Android 4.4.3 hit all compatible Google Play Edition devices, including the One (M7) and One (M8).
My Civil Partner has HTC One M7 32GB Locked to Vodafone. He his getting call dropouts when on a phone call to me (I am on Google Nexus 5 (Open Phone also on Vodafone) which is on Android 4.4.4. I believe it it the M7 at fault as its on Android...
Jeddah, KS. Arabia; My Z Ultra got Android 4.4.4; just for your knowledge. Thanks