Introduced in late 2014 with Android 4.4 KitKat on board, the Desire Eye currently runs Android Lollipop with Sense 6.0 UI, following an update released in the summer of 2015.
The HTC Desire Eye is available in many parts of the world, including in the US, where AT&T is selling it starting at $9.34 per month, or $279.99 outright.
As you may have heard until now, Android Marshmallow brings significant improvements over Lollipop, including longer battery life (thanks to what Google is calling Doze mode), Now on Tap (offering contextual information based on what's on your screen), individual app permissions, and so on. As for the HTC Desire Eye, you can find out more about the smartphone by reading our review of it.
HTC Desire EYE