Spotify plans to celebrate reaching 10 million users later this month, according to a party invite sent to press and analysts.

That’s certainly an impressive milestone for the ad-supported streaming music service. But it’s not clear whether those are 10 million active users or just 10 million registered accounts.

It’s also not clear how many are now paying the monthly subscription fee for Spotify’s premium tier. In July, founder and CEO Daniel Ek pointed to a subscriber figure of 500,000.