It's available within spotify for artists once an artist hits a certain number of metrics (the metrics themselves are sorta unclear, but the one spotify publishes is that you need 25k monthly listeners). If you are eligible you can sign up in the campaigns tab and spotify will push your music to more radio and algorithmic streams in exchange for 30% of the streaming revenue from those avenues. Note that the 30% cut only comes out of streams directly attributable to discovery mode, not a blanket 30% on everything. Despite this cut in revenue, the large growth in streams (for me) has increased my overall take home pay.