Four months after Billboard first reported that Amazon was set to debut a new, full-featured streaming service oriented directly towards its Echo smart speaker and the personal assistant named Alexa which powers it, that new service has arrived. It's called Amazon Music Unlimited.

Amazon already had a music streaming service, Prime Music, which launched two years ago with a relatively small catalog -- around two million songs compared to the 35-million-plus available on Spotify, for example. Unlimited, however, will expand that catalog to the level of Spotify and its other competitors -- and presents a significant uphill battle for "Big Green" and the others when trying to woo Echo owners.

If you already say "Hey, Alexa" on a regular basis, you'll pay $3.99 per month to connect your Echo device to Music Unlimited (this price point excludes use of the service on any other device). Prime members will be able to subscribe to Unlimited for an additional $7.99 per month, or $79.99 per year. Those without either can pay $9.99 per year for the service, equivalent to Spotify, Apple Music and Tidal's ad-free tiers. (And, presumably, Pandora's upcoming service as well.)

Music Unlimited arrives at an auspicious time for the streaming market. Just two weeks ago, it was validated stateside by a report from the RIAA, which attributed an 8.1 percent growth for the overall recording industry to the sector. As well, competition between its major players has gone from a simmer to a boil over both exclusives -- now outlawed by Universal Music -- and helping casual listeners with new music discovery, a perennial problem when your catalog would take at least 171 years to listen to (if you listened non-stop).

Boom knows.

"Music has always been central to the experience on Echo, and given its success, we really wanted to invest more heavily and further extend the lead we had established [with Echo]," Amazon's head of music Steve Boom tells Billboard. "We've worked very hard to make [Unlimited] more fun and easier to use than the other services in the market."

A big part of that is the work Amazon put into Alexa. In addition to asking for specific songs or albums, Alexa will also be able to respond to queries like "Play the new Green Day song" and come up with the band's latest single. ("You're not asking for their newest song, but rather the one being newly promoted to radio, for example," Boom says. "The simpler it is for the consumer, usually the more complicated it is on the back end," Boom explains. "We had to invest a lot in both metadata and machine learning, which means computer science to understand various attributes about music. The way people describe music is information that isn't readily available.").

Alexa can also can match lyric snippets to hit songs, and can pull up playlists by request based on decades, eras, moods or specific situations based on a user's listening history ("Play pop music from the '80s," or "Play Pearl Jam's catalog from 1991-1994"). Amazon is also debuting a sort of "podcast liner notes" program called "Side to Side," wherein artists such as Sting, OneRepublic, the Chainsmokers, Jason Aldean and Lindsey Sterling, for example, will explain the backstory of their work alongside their songs.

"There's a reason we're focused on the voice experience -- we believe music streaming is entering a new phase," Boom says. "Historically, it's been driven mostly by smartphones, but we believe quite strongly that there's a new phase of growth coming for the music industry, and that's connected smart devices. We wanted to really double down on our investment in voice and extend Amazon's lead in the home."

The pricing plan is also significant, particularly in a music industry that has insisted on keeping the bar for unlimited listening at $9.99 for streaming services.

"From our perspective, with Prime we helped push the music industry away from the one-size-fits all approach to music streaming, and to go after different customer segments," Boom says when asked about negotiations around that $3.99 price point. "But more important than that, [the industry] sees the importance and the promise of the voice interface in the home.

"We're going to grow the market [and add] new customers to streaming with a great way to get into streaming with really low friction, and at some point those customers may say, 'I also want this.'"

For Unlimited, Amazon has deals in place with all three major labels as well as hundreds of indies, according to Boom, and the service is expected to expand into the U.K., Germany and Australia before the end of the year. But there's still the issue of cost; Spotify, Pandora and other full-service streaming services have all failed to turn a profit to date.

"Amazon has always been in the music business, and has focused on making music a profitable business on its own two feet," Boom says. "Obviously, the investment required to build a compelling streaming service, with machine learning, all the new frontiers around voice -- it's very expensive. That being said, we are running a music service. And we want to make music profitable inside Amazon."