https://www.theverge.com/2017/11/2/16597248/samsung-beta-android-oreo-program-galaxy-live

The Samsung Experience 9.0 is now live bringing a beta version of the Android Oreo operating system to Galaxy S8 or S8 Plus owners in the US, UK, and South Korea. Testers provide feedback about performance, stability, and usability in return for being first to use the new OS tweaked to Samsung’s liking. The program helps Samsung develop experiences across mobile software, apps, and other services before their official release.

Users wanting access must have a Samsung Account and meet specific requirements. For those in the US, beta testers must be on Sprint or T-Mobile network devices, or have an unlocked device with SIMs from these carriers. Those in the UK must have an unlocked device.