Finished the Two Sigma onsite last month for a senior SWE role on the quant-tech side. Four-hour block, five rounds back to back with short breaks. Here's the actual structure and what each round felt like.
Round 1: Coding (45 min). One problem, algorithmic. DP-adjacent. They wanted optimal solution and asked me to walk through time/space complexity formally. Not "oh yeah n log n" casually, actually prove it.
Round 2: System Design (60 min). I wrote up the system design round in a separate post so I'll keep it short here. High-frequency data pipeline, pushed hard on failure modes and cost reasoning.
Round 3: Behavioral (45 min). More substantive than expected. Real probing on disagreement, uncertainty handling. Not a soft conversation.
Round 4: Domain deep-dive (45 min). This one felt more like a second lighter system design or a technical discussion. My background is distributed systems so we went deep on consensus protocols for about 20 minutes. I wasn't expecting that but it was genuinely interesting.
Round 5: "Culture fit" with a senior person (30 min). Honestly the least structured round. More conversational. They asked about career trajectory and what I find intellectually engaging. I got the sense this was partly checking whether I'd be good to work with day to day.
Interviewers: generally sharp. One was clearly from the research side and thought differently about tradeoffs than I'm used to. Not bad, just a different frame.
Pace: intense. Five rounds back to back is a lot. I'd eaten beforehand but still flagged around round 4. If you have a choice, take the breaks seriously.
Timeline: received offer ~10 business days after the onsite. One debrief call with the recruiter after where they gave some calibrated feedback, which was unusual and appreciated.
Is it worth it? Comp was strong and the people I talked to seemed genuinely engaged in their work. Different vibe from product companies in a way I found appealing after FAANG burnout.