The Android Oreo update has been released for more versions of the Samsung Galaxy S8 recently, the latest devices to get it is the AT&T version of the handset.
The update was recently released for the T-Mobile version of the handsets and now it is the AT&T version of the Galaxy S8.
The Android 8.0 Oreo update has only been released for the Galaxy S8 on AT&T so far, it is also coming to the S8 Plus and this update should start soon.
The update for the Samsung Galayx S8 on AT&T is around 1.5GB in size. It brings a wide range of new features to the handset. You can check to see if it is available on your device from the settings menu by going to Settings > System Update.
Source Droid Life