Update: It looks like users can unlock the AT&T version of the HTC One M8 with the HTCdev unlock tool, at least for the time being. A build of TWRP for the AT&T model is already available on XDA. Hat tip to Google+ reader Brian Haslip.
Wow, developers aren't wasting any time when it comes to cracking open new high-end hardware. Just a few days after a root method was released for the Galaxy S5, the folks at Team Win Recovery Project have already prepared TWRP for both the international and Sprint models of the new HTC One M8.