It's not a hard interview, first I was contacted by their project lead, then we had a phone interview, and a following 4-round remote onsite interview. I got a really positive feedback so their HR decided to move forward, but the following interview process was really slow since I need to talk with their very important people. So one week later I talked with their director of engineer, their lead HR and their COO in the end. In the end, their HR told I passed but it's two weeks later that I got the official offer letter.