This was a relatively minor update with only one item listed in the change log, and that was Prime Reading.
Yes, Amazon has made its month-old teaser ebook service available to iPhone-using Amazon Prime subscribers. (This feature is US only, of course.)
Introducing Prime Reading – a great new benefit for Prime members in the US Prime members can now enjoy unlimited reading from a rotating selection of over 1,000 Kindle books, current magazines, short works, comics, children’s books and more - all at no additional cost and with no due dates.
You can find the app in iTunes.