Three rounds:
1. Machine learning questions, easy to medium difficulty. Mostly conceptual, and some applied stuff.
2. Paid take-home exercise from one of their ML-heavy open-source GitHub repos. My specific problem was quite hard, and took me over a week of part-time work. Compensation for this was adequate, and in the end (as I got the offer) my solution was eventually merged as a product feature, which I found cool.
3. If your solution is good, a third round would have you closely discuss your approach with an ML engineer on their end. Trade-offs, alternatives, behavior, results, etc.
