Arriving alongside Android 8.0 is a beta version of Samsung Experience 9.0. Samsung Experience used to be called TouchWiz and is essentially the company's own UI that runs over the top of Android.
Samsung itself hasn't listed the changes introduced with Experience 9.0, but SamMobile has provided a full changelog of new features. Updates include being able to manage notifications for supported individual apps in the Quick Panel, the position of the Edge panel can now be changed by pressing and holding on it and higher-quality Bluetooth audio codecs including AAC and Sony's LDAC are supported.
To install the Samsung Experience 9.0 beta on your Galaxy S8 or S8+, you will need to enroll onto Samsung's beta program and have an active Samsung account. In the UK, the beta update will only be available for unlocked devices while in the US, unlocked devices and those on Sprint or T-Mobile are supported.
At 1.4GB, it's quite a large file, so make sure you have enough free storage on your phone and Samsung recommends carrying out a full backup of your phone before you go downloading and installing the beta software. Samsung hasn't said when a full global rollout of the final version of Experience 9.0 will be available.