AT&T has approved the update to Android 6.0.1 Marshmallow today for the Samsung Galaxy S6 Active. The update will arrive as software build UCU3CPE4 through a file that is roughly 1.4GB in size.
AT&T isn’t divulging any of the dirty details, but you should expect to see access to Google Now on Tap, Doze Mode (for better battery life), and better app permissions controls. I wouldn’t be shocked if you also get the latest UI update that came with recent Note updates.
To check for the update, head into Settings>System>About Device>Software Update>Check for updates.