Looks like we've got the answer to the question of which U.S. Samsung Galaxy S 4 variant will receive its Android 4.3 update next. Following updates for the Verizon, Sprint and U.S. Cellular Galaxy S 4s, reports have begun popping up about a similar update for AT&T's Galaxy S 4. Several users on Android Central and the xda-developers forums have successfully installed an 719.16MB update that bumped them up to Android 4.3 and software build number JSS15J.1337UCUEMJ9.
Neither AT&T nor Samsung have made any announcements about the update, so as of now we're still without an official changelog for this MJ9 update. However, Samsung has previously said that the Premium Suite update includes a bump up to Android 4.3, Galaxy Gear compatibility, Samsung Knox support and a few other goodies.
If you're rocking an AT&T-flavored Galaxy S 4 and haven't received an Android 4.3 update of your own, you can check for it manually by heading into Settings > More > About device > Software update > Check for updates. Considering the size of the update, you'll likely want to stick close to a Wi-Fi connection and set aside a few extra minutes to let the installation complete. One way to spend those minutes? Stopping by the comments section below and sharing the news of the update's arrival with everyone, of course.