Samsung Galaxy S4 owners on AT&T can start doing a happy dance now. The Android 4.3 update, version I337UCUEMJ9, is being pushed out to your device. Of course, as usual, it will roll out in chunks. This update already hit Verizon and Sprint. This is a bit surprising considering Big Red is usually the last carrier to get new updates. The update is a massive 719 MB so you will probably want to get it over WiFi.
This update gives you support for using the SGS4 with the Galaxy Gear smartwatch as well as Samsung's Knox security.