It should be pretty clear to everyone that you need to prep stories to behavioral interview questions stemming from the Leadership Principles. I prepped 8 stories and made sure I knew EVERYTHING about them. In one instance, an interviewer was checking my math in real-time as I was talking about the results. Expect them to push you. It is hard and intimidating but it isn't because they doubt your results they just want to see how much you know. In general the Amazon interview is definitely the most difficult interview process I've every participated in so know that and come prepared to kill it. I studied my stories, interview math, and case-based questions for at least 100-hours prior to my in-person loop. That is how much time I spent, you are very different so prep until YOU feel comfortable. The in-person interview was actually easier than I expected because I had prepared SO much but it was still incredibly difficult. I'd highly recommend any of the Lewis Lin case-based interview books, they were very helpful (I wasn't paid to say that, I was just introduced to him during my MBA program and his books helped a lot).
One last comment is around the actual job offer. I wasn't selected for the job I initially applied for, my guess was because I wasn't at the level of the job; however, my interviewers still felt I was a good fit for Amazon. The recruiter emailed me the day I was told I didn't get the job and asked if I'd be interested in a different position on the same team. None of my Amazon contacts had ever heard of this occurring before which is why I wanted to write about it. It is possible to not get the job but still be a good fit for Amazon. Following the contact from the recruiter I "re-looped" with the new hiring manager for one-hour and was then offered the new position.