Shortly after Android 6.0 made its debut late last month, HTC released a list of smartphones that it said will receive the Marshmallow update. In that list, the company specifically mentioned that its One M9 and One M8 smartphones would get the update towards the end of this year.
However, it now looks like the One M8 could get Android 6.0 a bit sooner given that the update for the handset has been certified by Bluetooth SIG. As you can see in the screenshot above, the certification was issued on October 28.
Keep in mind that we're just speculating an early arrival of the update as neither the Bluetooth SIG filing contains any specific date related to the roll out, nor there is any other proof of the same.