It looks like AT&T and T-Mobile are gearing up to push Android 4.4. and Sense 5.5 to their respective variants of the HTC one, according to HTC Executive Product Manager @moversi.

T-Mobile HTC One Owners! We have received technical approval for 4.4 OS + Sense 5.5! Expect the OTA out shortly! Thank you for your patience

— Mo (@moversi) February 21, 2014

Another Great News! We have received AT&T's technical approval for the HTC One w/4.4 + Sense 5.5.