No, it's not Android 5.1. That anticipated update hasn't shown up for the device anywhere except Russia yet, and today's update for the AT&T model is a minor one that keeps the Android version on 5.0.1. The OTA is a 142 MB download (the firmware version is N910AUCU2COC5) and brings enhancements to Find My Mobile, Reactivation Lock, and “Android OS security.” Yep, that's about it.
The update should be showing up on your Galaxy Note 4 of its own accord in the next couple of days, but you can also try to make it show up instantly by mashing the Check now button in the Settings » About device » Software updates menu on the phone. A Wi-Fi network is needed for downloading the update for now, so make sure you connect to one before you start waiting for that OTA notification.
Thanks, Nick Perperas!
