kindle-matchbook1Amazon has inadvertently revealed plans for a major new addition to its Kindle business — a monthly subscription for e-books.

As spotted by GigaOM this morning, Amazon put up a page that introduced a subscription service called “Kindle Unlimited,” which offers access to more than 600,000 titles and thousands of audiobooks on any device for $9.99 month.

Amazon has since taken the page down, but you can see a cached version below:

kindleunlimited2

The program is similar to Oyster, which bills itself as the “Netflix of e-books,” and allows users to read as many books as they’d like from the company’s library on iOS and Android devices, in addition to Amazon’s Kindle Fire line and the Nook HD.

oyster-readerThe service, recently featured as GeekWire’s App of the Week, includes more than 500,000 books and costs $9.95 a month.

Amazon already lets its Prime members, who pay $99 per year, borrow one free Kindle title per month. But if the company moves ahead with the “Kindle Unlimited” idea — given its large library and huge customer base — it could mean trouble for Oyster and similar competitors in the e-book subscription market.

We’ve contacted Amazon to see if the company is providing any other details about the plan.

Update, 10:45 p.m.: We spoke briefly with Oyster CEO Eric Stromberg, who said that his company is not surprised by Amazon’s move and is actually excited about it.

“They have pivoted from transactional to subscription-based in other media, and have had limited success,” he said. “They really paved the way in e-books, and it’s exciting to see them embrace the market we created as the future of books.”

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