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You exist long enough as a subscription service, and eventually you'll get a "+." Kindle Unlimited, Amazon's subscription service for borrowing books, comics and magazines, is the latest service to fall. In an email to subscribers, Amazon said it's renaming the subscription to Kindle+ and expanding its library of audiobooks.

The service still offers access to the same reading material, and now "thousands more audiobooks," according to Amazon. Amazon also says reading history, bookmarks, notes and saved titles all carry over to Kindle+, and it'll still cost $12 per month and limit borrowing to 20 titles at a time.

Really, the only thing that's meaningfully changing is the audiobook library. One of the ways Amazon is expanding its existing collection is by allowing authors who self-publish through the company's Kindle Direct Publishing platform to include their audiobooks in the service. Self-published authors have the option to upload traditionally produced audiobooks, and Amazon is also testing a service that can generate audiobooks read by a "virtual voice."

Kindle+ is live now and should work just as well through Amazon's Kindle app as it does on the company's redesigned lineup of Kindle hardware.