Got rejected after the Jane Street final round last month. Quant SWE track, 2026 grad. I've had a few weeks to sit with it and I want to write down what I think went wrong, partly for myself and partly because I couldn't find much honest post-mortem content when I was prepping.
What the loop looked like: OCaml coding screen, a second coding round focused on functional style, a probability/trading round, and a systems round. Four stages, multiple interviewers each.
Where I think I lost it:
OCaml. I knew it was coming and I still wasn't fluent enough. I can read it but writing under pressure in an unfamiliar functional style was painful. I was slow. They value fluency, not just ability to figure it out eventually. If you haven't shipped real OCaml code, start earlier than I did.
Probability round. I choked on a relatively standard expected value problem because I tried to set up a formal solution before I reasoned through the simple case. The interviewer gave me a hint and I recovered, but you can feel when the energy in the room shifts. The recovery probably didn't look great.
Didn't think out loud enough. Jane Street values how you reason, not just whether you get the answer. I got a couple of answers right but I was too quiet getting there. I think I lost points on process.
What I'd do differently: spend at least 6-8 weeks on OCaml specifically, not just reading docs but actually building something. Pair that with serious probability and market-making problems from the Jane Street puzzle archive. And practice narrating your thinking even when you're figuring something out.
I'm reapplying when the next cycle opens. No shame in that.