HTC One M9 starts getting Android 7.0 Nougat update at AT&T7
Well, starting May 16, AT&T customers who own the HTC One M9 can download Android 7.0 Nougat on their smartphones. The carrier mentions the update weighs in at around 1.4GB, so make sure you have enough storage before attempting to download it.
Unfortunately, the changelog is pretty short and contains a single mention, and that's the fact that the update includes the February security patch apart from all the new features and improvements brought by Android Nougat.
The update is pushed OTA (over the air) in waves, so if it doesn't show up on your phone right away, you can manually search for it by heading to Settings / About phone / Software updates.