After promising that their flagship phone, the HTC One, would get KitKat only 90 days after release, HTC has officially rolled out the update to owners of the Sprint variant of the phone.
Update 4.06.651.4 includes Android 4.4 KitKat and still includes Sense 5.5. The update is not yet available to everyone, but will roll out to everyone starting February 11th. Until you need to make a “customer request” to Sprint for the update.
If you are on other carriers with the HTC One keep an eye out for your update as HTC has submitted it to carriers for review.