14 DAY TRIAL // It looks like T-Mobile is now one of the last carriers that has yet to offer an Android 4.3 update for HTC One devices. The upgrade has already reached AT&T users and is now being deployed at C Spire Wireless.
As AndroidPolice points out, the major update to Android 4.3 Jelly Bean has been confirmed by HTC on its official website and aside from the said upgrade, HTC One from C Spire will also receive some bug fixes.
Software version 2.04.563.3 is now pushed OTA (over the air) to all HTC One devices at C Spire Wireless, but the rollout is made in stages so it may take some time before all smartphones receive it.
In order to manually check for availability, simply head over to Settings / About / Software updates / Check now and tap OK if you are eligible for the upgrade.