According to a recent tweet by HTC’s Mo Versi, it looks like the update will be making its way to your devices come 16th February. “Happy Friday! Good news for T-Mobile HTC One (M9) owners! We’ve received technical approval on Marshmallow, with the OTA to start on 2/16.” So if you do own a HTC One M9 under T-Mobile’s network, make sure you have enough storage so that the update can install itself.
As for AT&T’s update, Versi did tweet several weeks ago that the AT&T Marshmallow update for the HTC One M9 was expected to follow the Sprint release a couple of weeks later, but it still has to surface. According to Versi, apparently it seems there were some problems that has led to its delay.
“Yes, complications arose, requiring a new SW spin. I’ll let you know when it’s ready. Thanks for your patience.” Unfortunately no word on when the update will be pushed out, but either way T-Mobile customers can look forward to theirs next week.