Oreo for LG G6 has started hitting both unlocked as well as AT&T units in the US. While the update for unlocked models arrives as software version US99720a, that for AT&T models carries a version of H87120c.
Unlocked units also get May security patch included in the update. On the other hand, AT&T G6 models are on April security level. AT&T is yet to update its website to reflect the roll out, but we expect that happen to soon.