Samsung announced an Oreo beta for the Galaxy S8 and S8+ a few weeks ago and has been updating it pretty regularly since. A second beta was released a little over a week ago, and now a third one is out. There's only one truly new feature, but a lot of fixes are present.
The update, which carries build numbers G95xFXXU1ZQKG and G95xFOXM1ZQKG depending on region, weighs in at a hair over 623MB. It brings the November security patches, improved Bluetooth stability, and the option to hide the 'Apps running in background' notification.
There are quite a few fixes, which you can read in the very long scrolling screenshot above (tap to expand it). Most of them concern slow or delayed actions, but weak WiFi, Samsung Pass biometric authentication, and not being able to open the camera on the lockscreen, among others, have also been resolved.
To get this latest update, head into settings and check for updates manually. Given the amount of improvements, it'd be silly not to.