After a few months of beta testing, Samsung has finally begun rolling out the official Android 8.0 Oreo update to the Galaxy S8 and S8+. It's been almost six months since the first public version of Oreo was released to the original Pixel, but then again, it's not like we aren't already used to slow rollouts anyway.
The update will be rolling out first to beta testers, with regular users who didn't sign up for the beta to begin receiving the upgrade within the next 24 hours. The availability should vary by region and will be expanding over the next few days, so be sure to keep bashing that "Software update" button.
As we were expecting, the new update doesn't support Project Treble, as that is only guaranteed on devices which ship with Oreo out-of-the-box. Given that the S8 and S8+ launched with Nougat, it was unlikely that they would ever have been updated to support Treble, even if there was some reason to hope they could have.
Samsung has stopped the rollout due to some devices experiencing unexpected reboots.