The ZTE Maven 2 is one of many phones offered on AT&T PREPAID (previously AT&T GoPhone), and currently goes for $39.99 from the carrier. It has the specifications to match - a 480x854 display, a Snapdragon 210 processor, and 1GB of RAM. Still, this super cheap phone has one thing the Galaxy S8 doesn't have - Android 7.1.1.
AT&T is rolling out a software update to the Maven 2, jumping the system version from 6.0 to 7.1.1. The OTA clocks in at 1.16GB, and comes with the June 1 security patch level. The included AT&T Address Book application has been removed, and AT&T App Select has been added (which installs apps on your phone without your permission, yay carrier bloatware!)
To download the update, you must have a Wi-Fi connection and have the previous software update already installed (Z831V1.0.0B19). You can find more information at the source link below. You may need to view the page in Incognito mode, as AT&T's site is a bit wonky.