The Swedish startup confirmed the news on its web site:

They did not yet publish specifics about the pricing, terms of service or the size of their US music catalog, but you’ll know when we know. This will be huge. For the first time ever, iTunes will be under tremendous pressure to come out with a subscription-based music service because Spotify lets you stream music on an unlimited basis for a single-digit monthly fee, it’s in the cloud and available to any connected device and you can even mark songs for offline access.

Invites here.