Unsurprisingly, there's no way of knowing what's included in the update - while it's available, Microsoft hasn't provided any details about it on the Surface Studio update history page. The last update that it shows was from April 18, which enabled "Wake On Voice from Modern Standby".
Like April's update, today's is only for users that have the Windows 10 Creators Update installed. This can be seen from the updated Surface Studio Drivers and Firmware bundle that's available (in case you want to manually install it), as it shows a 15063 build number in the file name.
It's unclear why Microsoft struggles so much with publishing changelogs at the same time that it releases an update, but this is to be expected at this point. We'll likely find out what was included within the next couple of days.