Hi @hullgoddess!
Since licensing regulations require a Pandora Premium subscription in order to be able to listen to your station in "Artist Only" mode, free listeners and Pandora Plus subscribers will be able to view an advertisement in order to initiate a complimentary Premium Access session.
Those that do will also have access to Pandora Premium's other features during their Premium Access session.
For more info on how Premium session work, please visit our help page here.
Thanks for posting!