AT&T HTC One Official Android 4.3 OTA update has already rolled out and comes in the form of firmware build 3.17.502.3. Those who might be looking for the stock RUU 3.17.502.3 ROM Update Utility software tool for manual upgrading or for those who might want to restore back their HTC One devices to the original stock firmware, you can do so by simply running the stock RUU 3.17.502.3 in your computer. All you need is the HTC sync manager to install the necessary drivers in your computer.
Download the Stock RUU 3.17.502.3 from HTC
This update brings the new HTC Sense 5.0 UI and fixes for previous bugs. It is always ideal and highly recommended to have flashed the latest firmware on your device to boost better performance and system stability. I also highly advice to most HTC One advance users that you should have a copy of the official RUU, since it is very useful just in-case if you need to restore back your device to stock from custom ROMs, as well as your last resort for fixing soft-bricks if you messed-up from tweaking.