The Galaxy S8 users are getting software version G950U1UEU5CRH3, and the S8+ users are receiving version G955U1UEU5CRH3.
You can also check for the update manually by heading into Settings > Software update > Download updates manually.
Dear Samsung! Are you cooking something for the Unlocked Galaxy S9/S9+ users in the US? Sadly, they are still on June 2018 security patch. Disappointed? Yes!