Samsung is now rolling out a new Android 8.0 Oreo Beta for the Galaxy S8 and S8 Plus. The new Oreo Beta is currently rolling out to users in India and the countries that were part of the second phase of the rollout.
The update brings January Android security patch, and bug fixes. It has software version ZRA5 and weighing in at around 595MB.
This is highly likely to be the last beta update, as the beta program is scheduled to end on January 15, which will be followed by a public roll out for the update. If you want to check, go to Settings > Software Update and select Download Updates manually.