The process was similar to big tech interviews. It started with an initial technical phone screen, followed by a half-day, 3-5 in-person (video) interview.

The interviewers were very pleasant and helpful throughout the interviews.

My problem was that at the time, I was very comfortable at my current job, and my apprehension for changing showed through (I think).

In retrospect, my recommendation for others is to be "hungry" and show that you can kick-ass. Be proud of your experience, but show some humility as well.

Typical tech interview coding, data structures, algorithms, and working with data.