Round 1 was a take-home HackerRank test where you make an API call and process the response data. Round 2 was to implement the turn-based logic for a board game, optionally with logic for a computer opponent. There were two interviewers to ask additional questions to test your understanding at the end. Round 3 was about how you would structure data for a payment processing system. There were two more interviewers to test your understanding / have you build additional complexity into the system. Round 4 was the CTO selling you on working at the company.