Last night, HTC's Mo Versi who is VP of Product Management - and normally keeps us up to date with OTA rollouts - announced that the HTC One M9 in Canada would be getting the update starting on Monday, January 18th. Versi also replied to a few other followers that the HTC One M8's Android 6.0 update is aiming to rollout in the middle of the week (around January 20th-21st). That's currently their target, so it's likely still in testing. Which means that it could be a bit later than the middle of next week, but that's what it's looking like right now. Additionally, T-Mobile is also slated to get their update on the One M8 as soon as the 25th of January. Versi says the update is still in the lab, but should be ready for rollout on January 25th.
Typically, Versi is right on target with rollouts of new versions of Android. So we should be seeing the One M8 starting to get its update pretty soon. HTC has a renewed software update schedule - in fact the HTC One A9 gets updated within 15 days of Nexus devices - and it appears that they are sticking to that with the One M8 as well. The HTC One M8 was announced back in March of 2014, effectively making it almost two years old now, and it's still getting Marshmallow. In fact, it's getting it before many flagships from 2015 have gotten it. Pretty impressive to say the least.
There's no word on when the AT&T and Verizon variants of the HTC One M8 will get their updates. Typically, AT&T and Verizon updates are a bit slower. As they like to put their OTA's through a more strict testing phase before rolling it out to their customers. Which is a good thing but also a bad thing, as it delays updates that everyone wants, and wants quickly. But it does typically iron out bugs and such before rolling out to everyone - of course a few still sneak in from time to time. As soon as we learn more about the other HTC One M8 variants getting updates, we'll be sure to let everyone know.