Not long ago, @evleaks (who almost always provides accurate details) referred to the M8 as the “0P6B”. Before that, the M8 appeared in a benchmark test as the 0P6B120. So an educated guess can only lead us to the conclusion that this is the next One.
The Bluetooth SIG reveals that the P6BXXX has software that’s been certified for three major US mobile carriers: Verizon, AT&T and T-Mobile. All three are already selling the 2013 HTC One, so we shouldn’t be surprised to see them offering the new model as well. As you can tell, Sprint isn’t mentioned here, but that doesn’t necessarily mean it won’t plan to launch the M8 at some point.
Like the original HTC One, the M8 / One 2 should be joined by a Mini and a dual SIM version later this year. We haven't heard anything about a maxi version, but that doesn't mean this can't be in the pipeline too.
Update: @evleaks tweeted about an M8 destined for AT&T, "among others", back in November.
source: Bluetooth SIG