Jane Street

Large Enterprises

Most of these Jane Street write-ups come from Software Engineers (25), then Data Scientists (17) and Machine Learning Engineers (10). The most reported rounds are the technical phone screen (44), the system design round (6), the onsite coding round (3) and the recruiter screen (1).

54 interview notes · updated Jul 2026

Jane Street·Software Engineer·Technical Phone Screen

Jul 2026

Jane Street software engineer interview with a probability brain teaser. The kind of question where you either see the structure quickly or spend five minutes going in circles.

In a three-player dice game where each person rolls a standard 6-sided die and the highest roll wins (with ties broken by re-rolling among tied players), your two friends have both rolled a 4. You roll next. What is the probability that you eventually win?

“I stared at this longer than I'd like to admit.”

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Jane Street·Machine Learning Engineer·Technical Phone Screen

Jul 2026

Jane Street ML Engineer interview, one meaty technical question that was basically a full project scoped into a single session. Felt more like a design review than a coding screen.

Given a time-series dataset, build an end-to-end ML solution to forecast future values. Walk through your model architecture choice, how you'd implement the training loop in PyTorch, and how you'd evaluate it.

“This is a lot to hold in your head at once.”

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Jane Street·Software Engineer·Recruiter / HR Screen

Jul 2026

Recruiter screen for a software engineer role at Jane Street. Just one question from what was shared, a standard motivation question, but Jane Street puts real weight on these so it's worth thinking through.

Why Jane Street? Walk us through what draws you to this firm and this role specifically, with concrete examples from your background.

“They want specifics, not vibes.”

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Jane Street·Data Scientist·Technical Phone Screen

Jul 2026

Jane Street data scientist interview with a pretty gnarly probability/game theory problem. One question, no fluff, just math and reasoning under pressure.

You roll a fair six-sided die repeatedly, accumulating a running sum. You can stop anytime and collect the current sum, but if the sum ever hits a perfect square (1, 4, 9, 16, ...) you lose everything and get zero. There's no roll limit. What's the optimal stopping strategy, and what's the expected payoff under that strategy starting from zero?

“This one wrecked me for the first few minutes.”

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Jane Street·Data Scientist·Technical Phone Screen

Jul 2026

Jane Street Data Scientist interview with a probability/game theory problem involving optimal dice strategy. The math is clean but the reasoning chain to get there is genuinely tricky, especially under pressure.

Alice rolls a fair 30-sided die and Bob rolls a fair 20-sided die. Whoever shows the higher number wins, with ties going to Bob. Bob can reroll once after seeing his first result, but he never sees Alice's number before deciding, and his second roll is binding. Assuming Bob plays optimally, what is the probability that Alice wins?

“This one took me a while to set up properly.”

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Jane Street·Data Scientist·Technical Phone Screen

Jul 2026

Two pretty intense quant/algo questions for a Data Scientist role at Jane Street. Both required actual derivations and working code, not just hand-waving. The kind of interview where you either know the math or you don't.

You're at position k in a 100-person queue when a second checkout counter opens. Each other customer independently moves to the new queue with probability 1/2, and if you also move, your spot among the movers is uniformly random. Both counters serve at the same rate. Derive your expected wait time for staying vs. switching, and find the threshold k where switching becomes the better choice.
Given an integer n in cents and coin denominations of 1, 5, 10, 25, and 100 cents, count the number of distinct combinations (order doesn't matter) that sum to exactly n. Formalize it, design an algorithm for n up to 10,000, and analyze time and space complexity.

“This one took me a while to set up properly.”

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Jane Street·Machine Learning Engineer·Technical Phone Screen

Jul 2026

Jane Street ML Engineer interview, one big technical question that basically covered everything you'd ever want to know about time series forecasting. It was a lot to hold in your head at once.

You're given a time-series dataset with timestamps and numeric targets. Walk through your full pipeline: preprocessing, modeling choices, evaluation strategy, and how you'd handle concept drift over time.

“This question is basically five questions glued together and they let you run with it.”

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Jane Street·Software Engineer·Onsite - System Design / Architecture

Jul 2026

Jane Street software engineering interview where I built a two-player piece-dropping game engine from scratch and then got asked how I'd productionize it as a library or API. The design follow-up was the real interview.

You've just coded a working game engine under time pressure as a single script. If you had to turn this into a library other engineers depend on, or expose it as a network API, what would you change and what would you add?
How would you add a new rule variant, like diagonal wins or a third player, without breaking existing users of the library?
If this became a network API, would you make the service stateful or stateless? What are the trade-offs?
Once other teams are depending on the library, how do you roll out a breaking change to the public interface?
If you only had time to write five tests before shipping, which behaviors would you pin down first?

“This is where I fumbled a bit.”

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Jane Street·Software Engineer·Technical Phone Screen

Jun 2026

Jane Street SWE interview with a two-part coding problem centered on building a collapsible code editor feature. The problem was more involved than it looked at first glance, especially the nesting independence requirement in part two.

Given a list of lines representing source code where each line has at most one brace as its last character, write a function that returns a mapping from each opening brace's line index to its matching closing brace's line index, in a single pass.
Extend the brace-matching solution with a toggle and getText interface that supports collapsing and expanding individual brace pairs, where each pair's collapsed state is fully independent regardless of nesting.

“Stack-based solution, pretty standard once you see it.”

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Jane Street·Machine Learning Engineer·Onsite - System Design / Architecture

Jun 2026

Jane Street ML Engineer interview with a pretty gnarly systems design question. Not the typical ML theory stuff I prepped for, which threw me off a bit. The question was open-ended enough that I kept second-guessing my own design choices throughout.

Design and implement a compiler or interpreter for a simple custom programming language. Walk through your object-oriented design, the compilation pipeline stages, and how you'd approach debugging and fixing errors in the system.

“This one took me a minute to even figure out where to start.”

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Jane Street interview FAQ

What rounds are in the Jane Street interview?

Candidates most often report a technical phone screen (44 write-ups), a system design round (6), an onsite coding round (3) and a recruiter screen (1).

What does the Jane Street technical phone screen cover?

Across 44 technical phone screen write-ups, the most tagged question topics are Algorithms & Data Structures (68 questions), Technical Trade-offs (56) and System Design (28).