Apple had been widely predicted to hit around 7.5m paying subscribers back in September, when many people's free trials would have come to an end.
While it's good news for Apple Music, Apple customers' uptake of streaming may in turn have an adverse affect on download revenues, with iTunes currently still a huge source of download sales.
Spotify hit 20 million paying users back in June 2015, making it the most popular paid-for service. Spotify had declared in December that it hoped to hit a total of 100m users, including people on the free tier, by the end of 2015.
It’s also been reported that Spotify may eventually reserve certain content for paying subscribers in response to some artists only wanting to partner with paid-only services such as Apple Music or Tidal. Of course others, like Adele, keep their new music off streaming services altogether - Adele's record-selling 25 album isn't available on any streaming service.
Either way, it looks like the popularity of music streaming services is only going up, with downloads and physical sales likely to drop.