After launching the beta program for the Galaxy Note8 yesterday, Samsung is now launching the Galaxy S8 and S8+ beta program as well. Owners of the two phones will be able to register and participate starting today. The Samsung Members app currently only accepts participants from India but we are sure other markets will get it soon enough. For instance, the Galaxy Note8's beta program opened up yesterday in India and South Korea but today United Kingdom also joined the list. Owners who are approved will get the beta firmware for the Galaxy S8 and S8+ with build numbers G950FXXU4ZSA5...
Source: https://www.gsmarena.com/samsung_kicks_off_galaxy_s8_s8_android_pie_beta_program_as_well-news-35103.php