Amazon is testing a service called "Kindle Unlimited" that would give subscribers unlimited access to e-books and audiobooks for $9.99 a month.
The company had published several pages on its website with information about the service, but it pulled them on Wednesday. The pages still exist in Google's cache, however, and a subsection of the Kindle Store labeled "KU Test" included over 638,000 titles as of Wednesday.
The Kindle Unlimited news was first reported by Gigaom; Amazon did not immediately respond to a request for comment.
If all those "KU Test" books end up being included in Amazon's subscription service, that would trounce the size of rivals' subscription reading libraries. Scribd, for instance, offers 400,000 titles on its book subscription service, which costs $8.99 a month. There are around 500,000 on Oyster, which is $9.95.
Of course, not all selections are created equal -- Oyster and Scribd have deals with major publishers like Simon & Schuster and HarperCollins, whose titles don't appear available at this point in the Kindle Unlimited section.
A HarperCollins spokeswoman said the publishing house is "not participating at this time" in Kindle Unlimited. As for the other "big five" publishers, Penguin Random House declined to comment; Macmillan, Hachette and Simon & Schuster did not respond to requests for comment.
Amazon has a contentious relationship with these publishers, having tangled with them repeatedly over pricing issues, so it could have trouble getting them to sign on for Kindle Unlimited.
The publishers reached settlements with the Justice Department in 2012 and 2013 over allegations that they conspired with Apple to team up against Amazon and fix the price of e-books. More recently, Amazon has been putting the screws to Hachette as part of a pricing dispute, removing pre-order options from Hachette books, cutting discounts and lengthening delivery times.
Rumors of an Amazon e-book subscription service have persisted for several months. Amazon already allows users of its Prime premium service to borrow one book each month for no extra charge. The company also offers subscription music and video services with Prime.