Online radio giant Pandora opened the gates Tuesday for anyone to join its long-planned Spotify-style music service, after inviting some listeners to test it last month.

Pandora Premium, a full-fledged, on-demand music subscription, will compete with faster-growing rivals like Spotify and Apple Music. Premium costs $10 a month, though the company is offering several free trials (see below).

Pandora, founded back in 2000, was a vanguard of music streaming with its digital version of radio and then quickly sprinted into the lead as smartphones emerged and grew in popularity. Despite that head start, Pandora's radio format locked it into rigid licensing rules that limited listener control: You couldn't pick the exact song you wanted to hear, and the service had to limit how many times you skipped a song that was playing.

Fresh competitors like Spotify and Apple Music arrived over the past decade and were able to strike more-modern song-licensing deals that allow customers to hear to whatever they want, as much as they want. Pandora's growth has slowed as consumers flocked to the more flexible services.

Pandora Premium gives the company a tier to compete directly with them. It's the company's first fully on-demand subscription, though it isn't Pandora's first subscription. In September, Pandora revamped its $5-a-month subscription called Plus, which removes ads and provides less-expansive perks, like a mode for listening offline.

Pandora is offering a variety of discounted or free trials for Premium. Current Pandora Plus subscribers who signed up directly on Pandora's website (as opposed through an app store) will get six months of Premium at the price they currently pay, no matter what that price is. They also must have a payment method all set up.

The length of a free trial depends on a few factors:

• 60 days free for people who aren't already paid Pandora subscribers of some sort, who set up a payment method and who sign up for Premium directly through Pandora.
• 30 days free for people who aren't already paid Pandora subscribers, who set up a payment method and who sign up indirectly, such as through an app store.
• 30 days free for existing Plus subscribers who signed up indirectly and have a payment set up.
• 30 days free for non-paying Pandora listeners who've already taken 30 days free of a Plus or Premium indirect trial and who become direct subscribers.

The service is available through Apple's App Store, Google's Play store or directly at Pandora.com/premium.

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