Kindle Unlimited isn't included with Prime. You will have to pay $12 per month after a 30-day trial. Only a small offering ...

Amazon Prime Reading is a free service for Prime members that allows ... letting you dive into a digital library packed with books, audiobooks, magazines, comic books, and more.

What's the deal: Amazon Prime members get more for their 30-day free trial. Instead of picking one audiobook with the free trial, Prime members can pick two with their complimentary credits.