After months of speculation, Amazon announced Friday that it was introducing a digital-subscription service that allows subscribers to download unlimited e-books and digital audiobooks for $9.99 a month.

The service, Kindle Unlimited, offers a Netflix style, all-you-can-read approach to a library of more than 600,000 e-books, including blockbuster series like “The Hunger Games” and “Diary of a Wimpy Kid,” nonfiction titles like Michael Lewis’ “Flash Boys,” and literary fiction and classics.

News of the service was reported earlier this week when Amazon accidentally posted a promotional video for the subscription model. The video was quickly taken down from Amazon’s website, but not before technology bloggers took notice.

So far, it appears that few of the biggest publishers will be making their titles available through the service. Books published by HarperCollins and Simon & Schuster, for example, are not offered, representatives from both companies confirmed. A spokesman for Penguin Random House declined to comment, but titles from the company’s 100-plus imprints are not currently available on Kindle Unlimited.

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When the service went live Friday morning, some popular titles were noticeably absent. Subscribers who want to read Laura Hillenbrand’s “Unbroken” or Veronica Roth’s “Divergent” won’t find those books on Kindle Unlimited, at least not yet. (Books that can be downloaded for free as part of the subscription have an orange “Kindle Unlimited” icon under the title, along with a $0.00 price tag.)

Amazon is also entering an increasingly crowded marketplace. It will be competing with publishing startups offering similar services, like Scribd and Oyster, which charge a similar subscription fee and have comparable digital libraries. Oyster has more than 500,000 titles available and gives readers unlimited access for around $10 a month. Scribd has about 400,000 titles and charges subscribers about $9 a month.

Oyster offers titles from six of the top 10 U.S. publishers, including some not offered through Kindle Unlimited, like HarperCollins and Simon & Schuster, according to a company representative.

But Amazon has a huge advantage with its vast audiobook library, which it is bundling into the subscription service. Amazon owns Audible, and is including 2,000 digital-audio titles in Kindle Unlimited.

Through the company’s Whispersync for Voice technology, users can toggle between digital audiobooks and e-books, alternately listening and reading without losing their place in the story.

That could ultimately prove to be the most appealing part of the service, as digital-audiobook sales continue to soar. According to a recent report from the Association of American Publishers, revenue from digital audiobooks continues to grow at a rate of more than 24 percent quarter over quarter.