In a surprise announcement on its Twitter account, HTC USA said that final KitKat software has entered carrier labs for final testing. They also noted that we should expect certification for all four major US carriers next week.
Certification is currently in the third of four stages involved in pushing out OTA OS updates to devices. Shortly after passing carrier certification, the update should start getting sent out to devices.
More progress should be announced next week, especially considering how transparent HTC has been with the update process as of late.