When it comes to the upgrade of Android to version 6.0 (also known as Android M or Marshmallow), it has been slow to come out on many Android devices, including those from HTC. The worst part is that HTC promised it by the end of 2015, but wasn't really able to deliver it until the first part of 2016, at least to its flagship phones. This is the latest news on the Android M Version 6.0 Release Date for HTC Upgrade for HTC One M9 and M8 for Verizon, Sprint, US Cellular, AT&T, and T-Mobile; Specs and Release Date for the HTC One M10 (or HTC 10).
First of all, Android M has come to the M9 on the T-Mobile, AT&T, and Verizon. As for the flagship from two years ago, the HTC One M8, it has been reported that it will come to T-Mobile and Verizon Wireless. It is common for some carriers to receive the Android upgrade before others, so if you have any of the flagship phones on any carrier like US Cellular, T-Mobile, Verizon, Sprint, and AT&T, then you should check the Settings menu for a System update for a possibility of an Over The Air (OTA) upgrade.
As for any upgrades to the HTC flagships, there has been some change on that front. The issue with HTC is that there simply was not news when it came to the other HTC devices such as the HTC Butterfly 3, HTC Desire 816, HTC Desire 820, HTC Desire 826, HTC One M9+, HTC One E8, HTC One M8 EYE, HTC One ME and HTC One E9. The good news is that according to the International Business Times, it would appear that Android 6.0 Marshmallow is "seeding" to the HTC Desire Eye, One E8, and One M8 Eye users, at least in specific regions. The One E8 is starting to roll out to users in China, and the One M8 Eye is rolling out in China and Europe. The Desire EYE is confirmed to get an Android 6.0.1 update as well.
According to Phone Arena, HTC is on the cusp of announcing its latest flagship phone, the HTC 10. Yes, it has been known by many names like the HTC One M10, the HTC M10, or the codeword of the HTC Perfume.
One thing that is for sure is that the newest HTC flagship phone will have Android 6.0 right out of the box. As for the rest, it is just rumors like a 12 Megapixel Ultra Pixel camera, and it will be "world first, world class". Other rumored features include 5.1 inch display (1440 x 2560 resolution), a Qualcomm high-end Snapdragon 820 processor, fingerprint scanner, 4 GB of RAM, and 64 GB of internal memory. Expect the announcement of the HTC 10 soon.