First round is a battery of online tests which you can find pretty easily online (tradermath). Second round (technical) was a 1-1 with a trader where we played a betting game. I was shown three categories, dice, cards, and coin flips, and I was given around $1000 and 5-7 possible bets each with separate betting ratios for each category. You are given three separate rounds, each with less time than the preceding one to make your bets. Ask questions, speak clearly, and don’t stress too much (I did none of these). Almost everyone will be overwhelmed, and that’s the point; a major part of quantitative trading is remaining calm under pressure, and every round tests that. From what I’ve read online, you’ll have an HR and an on-site after this, (I've also read of people having multiple technicals.) and the on-site is against other potential interns, each acting as a market maker. Best of luck, and if you don’t succeed, that’s okay, it’s not quant or nothing!