The endlessly-hyped music streaming service Spotify has only been live in the United States for less than four weeks, but is already boasting 1.4 million American users, according to AllThingsD.

About 175,000 of those users are paying for the service, which is a conversion rate of 12.5%. There was no word on the break-down of those paid subcriptions between Spotify’s $4.99 unlimited Web streaming plan and its $9.99 premium plan, which includes mobile access.

These numbers may do little to answer questions about the long-term viability of Spotify’s business model but they provide an early glimpse at the popularity of the service, the free version of which is currently only available by invite.

If it continues to grow at this rate, Business Insider points out, Spotify is on track to reach 20 million users in its first year, about three million of which would be paying for the service.

Of course, there’s no guarantee that the current rate of adoption will continue, especially considering the level of pre-hype launch garnered by the service, which had been a huge hit in Europe for a few years prior to its July 14th U.S. launch. Given that hype, it’s possible that many users opted to skip over the nail-biting wait for an invitation to the free version in favor of one of the paid subscriptions. Once the invite-only wall comes down, Spotify may well see a flood of new users, but will a comparable percentage of them continue to pay up?

Spotify will need to up the ante considerably if it’s serious about hitting the very ambitious 50 million user mark within its first year. That’s what was promised to advertisers prior to the service’s U.S. launch, according to marketing material leaked to AllThingsD in early July.