I went through the Jane Street final round last month for a mid-senior SWE role. One thing I didn't expect: they do have explicit behavioral rounds, and they're not treated as a formality. Sharing my notes.
Jane Street cares a lot about a few specific values that come through in both what they ask and how they respond to your answers.
Intellectual honesty. Multiple questions were designed to find out whether you'd say "I don't know" when you don't know. I got asked to estimate something I genuinely didn't know the answer to. I gave my reasoning and flagged my uncertainty. They seemed to like that. A friend who went through it said he tried to bluff on a similar question and could tell it went badly.
Rigor under pressure. One behavioral prompt was roughly: "tell me about a time you were wrong about something technical. what did you do." They pushed on whether I actually updated my view or just said I did.
Collaborative problem-solving. They asked me to describe a disagreement I had with a coworker about a design decision. They were explicitly watching for whether I framed it as "I was right" or whether I could describe the other person's reasoning fairly.
For a quant trading firm, the behavioral emphasis surprised me. But it makes sense: the cost of someone who can't acknowledge uncertainty in a trading environment is enormous.
On values: I looked this up before going in. They talk openly about "thinking clearly" and "being honest" as core to their culture. These are not just words on a wall. The behavioral rounds probe exactly these things.
One practical note: they do NOT want STAR-format robotic answers. More like a real conversation where they'll ask follow-up questions and expect you to engage. Have the actual details ready, not a rehearsed script.