Samsung has pushed out the Oreo update notes on the Exynos version of the Galaxy S8, which carries the model number SM-G950F. It's likely that the update notes will be the same for other models of the device but it is worth mentioning that there could be some differences. If you're unsure which model you have, the Samsung Galaxy S8 in the U.S. runs on a Qualcomm Snapdragon 835 processor and not Samsung's in-house Exynos chip, so the notes are for an international model.
As to what's changed, the most obvious and notable difference is that Oreo for the Galaxy S8 is introducing version 9.0 of the Samsung Experience UI software, which brings along its own set of changes in addition to those that come along with Android Oreo specifically. Of those changes there are improvements made to various things on the device like biometrics, the Quick Panel, the home screen, Samsung Keyboard and more. Some of these changes might be more useful to a wider audience than others, like the biometrics improvements which Samsung has added in so that the device offers better security. With these improvements it'll only be possible to use the biometrics with secure lock types, and they will be disabled if you use the swipe to unlock or don't have a screen lock set up at all.
Since this is Oreo, notification channels are included now which makes it easier to manage notifications on the device, though the app itself will also have to support notification channels so it's important to remember that the new options won't show up for notifications that come in for every single app. Other notable improvements are included with this update as well like better sizes and color for fonts on the edge screen, and of course better overall system performance. There is also now a feature called smart view available which makes the screen on the phone go black when it's mirroring to another screen, which should help battery life. Samsung officially released these updates notes yesterday so if you have this model of the device and haven't seen the update to Oreo yet then it may be just around the corner.