First round was an online test, similar to the GRE. Second round consisted of a couple back-to-back interviews with traders, one technical and one qualitative. One question I remember being asked was the 10x10x10 cube question (paint outside, what's P getting a painted face given x). Before the final round was a chance to meet CTC employees and hear directly from the founder on Zoom. There was an education session on market-making. The final round consisted of 4-5 interviews with various employees, covering a variety of areas pertinent to the job.