And now, as noted by Droid-Life, Samsung is issuing Android Oreo for the unlocked Galaxy S8 and Galaxy S8+ in the United States. The stable build for the Galaxy S8 is G950U1UEU2CRB9, while the build number for the Galaxy S8+ is G955U1UEU2CRB9. The updates have typically been over 1GB, so you will probably want to carve out some time before you download and install the new software.
As for what’s new, Samsung is making sure that biometric security measures can only be used if the owner has a secure screen lock in place. So basically, “features that use biometrics (face, fingerprints, and irises) are only available when you use a secure screen lock type (pattern, PIN, or password).” There are also app icon notification dots, the ability to long-press an app icon to get shortcuts, and much more.
The Android 8.0 Oreo update is rolling out now as an over-the-air (OTA) update, so it might take some time to show up on your device.