Thanks to the OTA update, T-Mobile users with the Moto X will need less time teaching the phone when to respond to the "Ok Google Now" verbal cue. Touchless controls are more accurate and responsive, and transferring content from your old Android phone to the Moto X is much easier.
Some bugs are also killed dead by the update including one that made your voice sound choppy to the person on the other end of a phone call. Another bug that could prevent the phone from reporting its position to the Moto Care Lost Device Finder service has been fixed. And for those who have their Moto X in their pocket during delicate brain surgery, a bug that caused the phone to read text messages and announce calls while not in Drive mode has been repaired. The new software version gives T-Mobile's Moto X users 30 days from installation of the update or the activation of the phone, to redeem the free 50GB of Google Drive storage being offered in a promotion.
Motorola suggests that your battery be at least 50% charged when you download and install the update. If you have not received a notification about the update, you can try to pull it out manually (what a image that conjures up) by going from Settings>About Phone>System Updates>Download>Install.
source: Motorola via AndroidCentral