We've asked Spotify about the number of paying subscribers, and it tells us that it doesn't have an update at the moment. It had 30 million subscribers back in March. If that count hasn't gone up as well, it'll suggest that the company is having trouble convincing people to move beyond the free tier. And that's a problem when Spotify's losses have only widened in recent years despite its runaway growth. While it's no mean feat to have that many people shelling out every month, the company needs more paying users if it's going to remain healthy in the long run.

This still makes Spotify the largest streaming service by far. Apple Music, for comparison, has 'just' 15 million subscribers as of June. The difference? Most of Spotify's rivals (including Apple) don't have free offerings outside of trial periods -- they're not hurting their bottom line to add more users. Spotify may be the most popular streaming service, but it's not necessarily the most sustainable.