It's gotten there by being very good at knowing what it does best. Now, to reach the next stages of profitability and long-term success, it has to amplify all that. The Swedish streaming service announced in a memo on Monday that it will begin allowing advertisers to sponsor its signature Discover Weekly playlist, which refreshes every week with custom history- and preference-based song recommendations for every user. The new sponsorship's in-playlist and native ads, which will be delivered to all users on the free tier, will kick off with a series from Microsoft tied to the software company's "Empowering Us All" artificial intelligence campaign. Spotify already offers brand sponsorships on some of its other editorial playlists, but until now it has kept Discover Weekly -- which is heralded by both fans and competitor services as its flagship feature, and draws more than 40 million users a month -- a more organic, unfettered experience.