Three of the Big Four carriers in the US have already rolled out Marshmallow to the HTC One M8 and M9 units on their network. So we can say the Marshmallow update for AT&T-branded M8 and M9s is already delayed.
Worse still, it has been revealed that the update has been hit by further delays. The revelation was made by the Taiwanese company’s VP of Product Management Mo Versi on Twitter.
The reason behind the delay wasn’t revealed, although given that HTC is claiming to get the approval in next couple of weeks, it’s reasonable to assume that either the problem wasn’t that big, or the company caught hold of it and sorted it out quickly.