Ahead of Apple’s iPhone event on September 7th, the company has begun rolling out new, personalized music playlists to Apple Music subscribers, who are beta testing the soon-to-be-released iOS 10 mobile operating system and macOS Sierra. Originally introduced at this year’s Worldwide Developers Conference in June, Apple Music’s new playlists are a direct challenge to Spotify, whose “Discover Weekly” playlist is so popular it saw 40 million users in its first year.