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Citadel / Citadel Securities quant interview questions

23 questions · 4 reported stages · 7 hiring locations

What does the Citadel / Citadel Securities quant interview involve?

The Citadel / Citadel Securities quant loop runs 4 stages: recruiter screen, technical screen, case / project, super day. It tests probability, statistics, machine learning, brainteaser above finance knowledge, and it is run across New York, London, Chicago, Hong Kong, San Francisco, Paris, Dubai / Abu Dhabi. The questions below are ours, written to rehearse the same reasoning.

What Citadel / Citadel Securities publishes about its hiring

Citadel Securities publishes its interview process in detail, including campus first rounds and a one-problem onsite for experienced engineers. Citadel (the hedge fund) is interviewed alongside it for campus quant research. Checked against the firm's own pages on 18 October 2026.

Verified: stated by the firm

Official process: Experienced engineers (Citadel Securities)

  1. Recruiter conversation
  2. Technical screen (coding)
  3. Onsite, four to five hours: design, programming, code review, approach

Estimate: our modelling and compilation

  • The 4-stage loop below is compiled from public sources and candidate reports, not published by Citadel / Citadel Securities as a single sequence.
  • Modelled mid-level total compensation, Quant Researcher: about $625k USD. A KnowQuant estimate, not an employer figure.
  • Modelled mid-level total compensation, Quant Trader: about $600k USD. A KnowQuant estimate, not an employer figure.
  • Modelled mid-level total compensation, Quant Developer: about $475k USD. A KnowQuant estimate, not an employer figure.
  • Modelled mid-level total compensation, Systematic Portfolio Manager: about $2000k USD. A KnowQuant estimate, not an employer figure.
  • The 23 practice questions are written by KnowQuant to rehearse the reasoning; they are not Citadel / Citadel Securities's questions.

Not stated by the firm

  • - The hedge fund's own stage list for experienced researchers and portfolio managers
  • - Pay ranges outside jurisdictions that require them

Citadel / Citadel Securities sources

Primary material read while writing this piece. Firm specific practices are attributed to the firm that published them and should not be read as industry wide.

The loop as candidates report it (compiled, not official)

Each round answers the question candidates actually ask, then points at the round that follows it.

  1. Stage 1Recruiter screen

    What happens in the recruiter screen at Citadel / Citadel Securities?

    Background, motivation and compensation expectations. It is stage 1 of 4 in the Citadel / Citadel Securities loop, and candidates who clear it move to the technical screen.

    Next step: Technical screen
  2. Stage 2Technical screen

    What happens in the technical screen at Citadel / Citadel Securities?

    Role-specific: statistics and modelling for research, systems and C++ for engineering. It is stage 2 of 4 in the Citadel / Citadel Securities loop, and candidates who clear it move to the case / project.

    Next step: Case / project
  3. Stage 3Case / project

    What happens in the case / project at Citadel / Citadel Securities?

    Often a data exercise or take-home research problem. It is stage 3 of 4 in the Citadel / Citadel Securities loop, and candidates who clear it move to the super day.

    Next step: Super day
  4. Stage 4Super day

    What happens in the super day at Citadel / Citadel Securities?

    Sequential interviews with researchers, engineers and business stakeholders. It is stage 4 of 4 in the Citadel / Citadel Securities loop and it is the final decision point.

    Next step: rehearse the practice set

Practice questions matched to this loop

Filtered to the topics Citadel / Citadel Securities draws on for the roles it hires: probability, statistics, machine learning, brainteaser, algorithms, c++ and systems, mental maths, market making. Written originally for this platform, so they rehearse the reasoning rather than republish anyone's question bank.

ProbabilityHardResearch round

You draw cards one at a time without replacement from a standard 52-card deck until the first ace appears. What is the expected number of cards drawn?

Market makingHardTrading round

You are quoting a market and get lifted five times in a row on the offer, in full size, by the same counterparty. Nothing else in the market has moved. What do you do?

StatisticsHardResearch round

Your alpha shows a strong in-sample relationship with next-day returns, but the effect halves out of sample. Give three explanations that are not overfitting.

AlgorithmsHardEngineering round

You receive a stream of order-book updates and must report the maximum trade price in the last N events at every step. How?

C++ and systemsHardEngineering round

Your median tick-to-trade latency is fine but the 99.9th percentile is ten times worse. Name the likely causes.

Machine learningHardResearch round

A gradient-boosted model predicts next-hour returns with an out-of-sample R² of 0.004. Is that useful?

BrainteaserHardFirst round

One hundred prisoners each open 50 of 100 boxes searching for their own number; all must succeed or all fail. What strategy beats a vanishingly small success rate?

ProbabilityStandardFirst round

Two people independently pick a real number uniformly from [0, 1]. What is the probability the two numbers differ by more than 0.25?

ProbabilityStandardFirst round

A random walk starts at 0 and moves +1 or −1 with equal probability each step. What is the probability it reaches +3 before it reaches −5?

Mental mathsStandardFirst round

Estimate the square root of 4,600 to one decimal place in under ten seconds.

Mental mathsStandardTrading round

A contract pays 100 if an event happens and 0 otherwise. It trades at 37. You think the true probability is 41%. You can trade 500 contracts. What is your expected edge?

Market makingStandardTrading round

I roll two fair six-sided dice and pay you the product. Make me a market, two wide.

Market makingStandardTrading round

Make a market on the number of petrol stations in the United Kingdom.

StatisticsStandardResearch round

You backtest 200 signals and the best one has a Sharpe ratio of 2.4. Should you trade it?

StatisticsStandardFirst round

Two return series each have a correlation of 0.6 with a third. What is the tightest bound you can put on their correlation with each other?

AlgorithmsStandardEngineering round

Design a data structure that supports insert, delete and get-random-element, all in expected O(1).

AlgorithmsStandardEngineering round

How would you implement a limit order book supporting add, cancel and match, and what is the complexity of each?

C++ and systemsStandardEngineering round

Why might std::unordered_map be a poor choice on a latency-critical hot path?

C++ and systemsStandardEngineering round

Explain false sharing and how you would detect it in a multi-threaded market data handler.

Machine learningStandardResearch round

Why is k-fold cross-validation usually wrong for financial time series, and what do you use instead?

BrainteaserStandardFirst round

You have 25 horses and a track that races five at a time, with no timer. What is the minimum number of races to find the fastest three?

ProbabilityWarm-upPhone screen

You flip a fair coin three times. Given that at least one flip came up heads, what is the probability all three were heads?

Mental mathsWarm-upPhone screen

What is 17 × 23, without writing anything down?

Citadel / Citadel Securities interview questions by city

The same loop, read against the local market: what the desk hires for, how the round is run there, and what a passed loop pays in the local currency.

Questions candidates ask about Citadel / Citadel Securities

How many interview stages does Citadel / Citadel Securities run?

4 published stages: recruiter screen, technical screen, case / project, super day. The sequence is the same across every office we track.

What topics does the Citadel / Citadel Securities quant interview test?

Mainly probability, statistics, machine learning, brainteaser. Citadel / Citadel Securities hires for 4 quant families, so the technical rounds are weighted to the role rather than to finance knowledge.

How hard is the Citadel / Citadel Securities quant interview?

Hard by market standards. Our practice set for this loop runs to 23 questions, sorted with the hardest first, and the backgrounds that clear the bar are typically phd research and top-tier engineering.

What does Citadel / Citadel Securities pay after a passed loop?

Citadel / Citadel Securities benchmarks at roughly 130% of the market figure for the same role and seniority. Published ranges are held per role, seniority and market in the local currency.

Where does Citadel / Citadel Securities hire quants?

New York, London, Chicago, Hong Kong, San Francisco, Paris, Dubai / Abu Dhabi. Each market carries its own benchmark in the local currency.

Are these real Citadel / Citadel Securities interview questions?

No. Stage detail is compiled from public sources and candidate reports and labelled as such. Every question is written originally for this platform to rehearse the same reasoning, so nothing here republishes a firm's own question bank.

How Citadel / Citadel Securities compares

Side by side on modelled pay, interview stages, offices and the roles each firm hires for.

Roles this loop leads to

Each one carries a published benchmark by seniority and market.

Backgrounds that clear this bar

  • -PhD research
  • -Top-tier engineering
  • -Lateral hires from peer platforms
Citadel / Citadel Securities firm profileEvery firm's loop

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Stage detail is compiled from public sources and candidate reports and is labelled as such. Questions are written originally for this platform. We do not republish any firm's proprietary interview questions.

Methodology

Figures are expressed as annual total compensation (base salary plus expected performance bonus) in the reference market's local currency, converted from a US dollar base. They describe typical market ranges rather than any individual offer, and exclude sign-on payments, deferred equity and carried interest. Portfolio-manager figures reflect formulaic profit-share arrangements and are therefore far more dispersed than any other role.

KnowQuantIndex 2026.1 · Updated September 2026

Modelled bands describe the market, not an individual offer. Where an employer states pay, the stated figure is used and labelled as such.

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The loop, the reasoning it tests, and what the role pays once you clear it.