Eddy Cue clarified that artists will not be paid at the streaming rate they are paid during users paid memberships. They will be paid at a different rate that isn't being disclosed: http://recode.net/2015/06/21/apple-says-it-will-pay-taylor-s... Also: "Cue says Apple will keep the existing royalty rates it has already hammered out with the three major music labels for subscribers."
That's during the free trial period. The higher rates remain once people are paid subscribers.
It's worth nothing that by "higher rates" we are talking about a hundredth of a cent per stream.