Back at Google I/O, Samsung and Google announced that Daydream VR support would be coming to the Galaxy S8 & S8+ this summer but never gave a concrete date until now.
The Google VR account on Google+ announced that the update to make the Galaxy S8 & S8+ Daydream-ready is rolling out now. Android Police pointed out that it seems like a server-side switch then an OTA update.
On Reddit user said that clearing the app data for the Google VR Services app will help enable Daydream support on the S8 & S8+.
Source: Google VR on Google+ via Android Police