Didn't get a notification, but Oreo update was available upon check for system update in Settings. I have Z2 Force on Verizon. Update downloaded swiftly, installed in background, and prompted for restart, finished in under fifteen minutes, perhaps less.
This was already a fast phone, but after update I'd swear it's running even snappier, unlocking, starting and switching between apps, loading photos and webpages. Even camera shots seem a little faster, but that could be my imagination.
Notification bar, Settings, and Phone app changes are most noticeable so far. I use (and love) Action Launcher so haven't yet tried Oreo home screens and icons.
Not crazy about the persistent notification about background apps running, e.g. Pebble app. Not sure if there's a setting page to disable that.