Using tools from HTC and existing methods for the international version, the AT&T HTC One has cracked open
Good news for some folks interested in the AT&T version of the HTC One -- the HTC Dev site will unlock your bootloader, and the methods used to root and install ClockWorkMod recovery are the same as the international version.
We mentioned a few days ago that a few people were lucky enough to get their HTC One early from AT&T, and of course that means that people have been working at opening it up. Some have been concerned that AT&T would have the device blocked from using the standard HTC bootloader unlocking tool, but that doesn't seem to be the case.
There are a few things to keep on mind if you plan to try this for yourself as soon as you get your HTC One. This procedure will wipe everything off your phone as part of the bootloader unlock process. Also, the Calculator, Flashlight, Ringtone Trimmer and Sound Recorder apps are deleted in the process. This doesn't sound like a very big deal, but the absence of these apps means the device won't pass a file integrity check and can no longer receive OTA updates.
In any case, this is good news for those waiting on their new HTC One from AT&T, and also like to tinker with things.
Source: XDA developers