AT&T is updating their version of the Samsung Galaxy S 4 as well. The update is said to remove lag on the device and not much else is known about the update. It most likely patches an exploit that allows you unlock the bootloader but that’s yet to be seen. Make sure your device has at least 50% battery life before starting the update and being connected to Wi-Fi won’t hurt either. If you’re worried about the update killing the unlock bootloader method, you don’t have to except the update.