Round 1: Basic probability questions. Just EV stuff, find strats that maximize EV Round 2: Same as Round 2, questions are a bit more challenging Round 3: Harder than R2, this time expect some game theory too (knowing what the Nash equilibrium is, etc). The question will be more open-ended and challenging, so make sure you clarify what exactly the interviewer wants. The interviewer will work with you and guide you in the right direction. I was rejected after Round 3 even though I solved the question with hints, but Round 4 is in-person and they make you fill out an immigration form if you're outside the US so make sure you can enter the states for R4.

Half an hour with two questions, one has three and the other has two sub-parts. When you get stuck, the interviewer will give you some thought directions. Not too difficult questions in general.