Started with two HR screens, just mostly confirming intent and what roles I wanted. 2 technical interviews, drilled into projects, talked about some optimization problems and a python coding problem.
Interview questions [1]
Question 1
Something about How would you optimize a game matchmaking system.
Great mentoring, very good patience. They asked a lot about basic advanced mathematics, combinatorial theory and probability. Although I did not perform very well I think, the PhD group leader helped me with the questions and I learnt a lot.