AT&T has released a new software update G950USQS5CRF5 for Galaxy S8 and update G955USQS5CRF5 for Samsung Galaxy S8 Plus. The update comes with Android July security patch. The latest Android July security patch fixes common vulnerabilities and exposures discovered in the Android operating system. In addition, there are device stability improvements, bug fixes and further enhancements for performance.
Software update G950USQS5CRF5 for Galaxy S8 and update G955USQS5CRF5 for Samsung Galaxy S8 Plus will gradually release to everyone. You can also check manually for updates, go to Settings > About device > System update.
Make sure you have enough charge on your device at least 60% to 70% before downloading the update.