Now there is a new version of Android that was announced by Google at their I/O developer's conference last week, but it will take a while before Android N rolls out the newer Android devices. The issue is that most Android devices, at least the newer ones from Samsung, LG, and HTC certainly have Android M (also known as Marshmallow or Version 6.0) already. This is the latest news about Android M 6.0 Marshmallow and Android N Release Date for HTC One M9, One M8, and HTC Desire Series on Sprint, Verizon, US Cellular, T-Mobile, and AT&T.
At this point, HTC is pretty much covered when it comes to their flagship phones from two years ago with the latest HTC 10 has Android M right out of the box, and when it comes to HTC One M9 and HTC One M8, it has showed up on all of the five carriers including AT&T.
It will not be coming to the HTC One M7, but what about the likes of the HTC one M9+, HTC One E9, HTC One ME, HTC One E8, HTC One M8 EYE, HTC Butterfly 3, HTC Desire 826, HTC Desire 820, and HTC Desire 816, as well as the One A9, Desire Eye, and One E9? Well, the Marshmallow upgrade is coming too for these non-flagship devices. There is a report on Android Authority that the Desire Eye, Desire 816, M8 Eye, and Desire 820 is starting to come out in the International versions. I suppose it will probably come to all versions of these devices in all countries in United States.
The safest bet is that if you have a recent HTC device, you might already have access to Marshmallow already, especially if you have a flagship. Just go to "Settings" and "System Update" to see if you can download the Over the Air (OTA) upgrade now. It is possible that the upgrade could be available on one carrier for the same phone and yet not on another, which has become a pattern for Android rollouts.
As far as Android N is concerned on HTC, there was an announcement made right after Google I/O 2016 saying that HTC will have the new firmware on the HTC 10, HTC One A9, and the HTC One M9, according to Android Pit. Confirmation would come later in the year when Google ships Android N to manufacturers. So, it could take a while, as Marshmallow didn't come out until the beginning of this year, so expect Android N on newer devices at the beginning of 2017.