The Galaxy S4 has been reaping the benefits of Android 4.3 for a while, and now it's the turn of its ruggedized sibling, the Galaxy S4 Active, to start taking the leap to the newer version of Android. AT&T has begun pushing the Android 4.3 update to the S4 Active over the air in a 772 MB package, which should bring all the usual goodies like OpenGL 3.0 and Bluetooth 4.0 LE support, Galaxy Gear compatibility, faster performance and RAM management, interface tweaks, new home screen and camera modes, and more.
As usual, it's going to be a few days before the update manages to trickle down to all users, though you can keep hitting that “Check now” button in the Settings » About phone » Software updates menu to try and force it to show up. Other carriers should begin rolling out the update (hopefully) in the coming weeks, along with the international variant of the device.