Citadel / Citadel Securities Interview ProcessTier 1

Multi-Strategy Hedge Fund + Market Maker · Miami, NYC, Chicago, London

97 practice questions → Apply at Citadel / Citadel Securities → Learn more about Citadel / Citadel Securities ↗ Report a question from your Citadel / Citadel Securities interview

498

problems

99 easy 296 medium 103 hard

hires: Quant Researcher, Quant Trader, Software Engineer, ML Engineer

Online Assessment

Citadel Securities' OA is auto-graded and differs sharply by track - a large rotating HackerRank coding pool for SWE, recruiter-sourced probability and stats screens for quant, a pandas/R datathon for data science, and a non-coding equity aptitude test.

Practice this round 73 problems Pro

Software Engineering

live

2017-10 -> 2026-01

SWE / SDE / NG internHackerRank70 min2 of ~40

Two coding problems drawn from a large rotating pool shared across the SWE, SDE and new-grad intern screens (often a resume-screen filter).

Maximize the Minimum Gap in a SubsequenceCodingMediumSolve →Most-Visited Position Across SprintsCodingEasySolve →Maximize Cards Bought Within a BudgetCodingEasySolve →Shortest Substring to Rewrite for a Balanced Gene StringCodingMediumSolve →see all 40 in the pool →

Quant Research / Quant Trading

current

2021-12 -> 2025-07

QR / QTphone screen / live + QT OA~15-question OA

Two formats are reported for the Citadel Securities trading OA. A July 2025 QT candidate describes about 15 fill-in-the-blank probability and statistics questions (other prep sites cite 30 minutes); older HackerRank sittings (2019-2020) ran 10 probability questions in four separately timed sections, 23 or 30 minutes in total. Both formats have timed replicas, alongside the recruiter-sourced QR phone-screen brain-teasers.

2025 QT format: free 5-question sampleThe 4 screenshotted questions are in the full run; the rest are generated in the same format.Pro 2025 QT format: 15 fill-in questions in 30 minutes (Pro)4 screenshotted questions plus generated ones in the same format.Pro Classic format: free 2-section sampleGenerated in the reported format, timed like the real test.Pro Classic format: 10 questions in 4 timed sections, 30 minutes (Pro)Generated in the reported format, timed like the real test.Pro see all 15 in the pool →

Data Science

current

2019 -> 2024

DatathonHackerRank60 min~18-question MCQ

A multiple-choice data-science round mixing pandas/R analysis with statistics, probability and ML theory; the 2024 version tests both Python and R rather than letting you pick one.

Take the timed assessmentReal reported OA questions, on the clockPro

Unlock the full interview funnel

The first stage is on us — you're seeing it in full. Unlock every later round, the must-do problems, and stage-by-stage prep across all 56 firms with QuantVault Pro.

56 firmsEvery stageMust-do problems

First-Round Phone Screen

45-60 min - video Round guide →

A 45-60 min remote interview blending technical and behavioural. Core technical: one coding question (LeetCode-medium, Python or C++) plus a probability/statistics question for quant tracks. Recruiter intro up front; they screen for correct, efficient code written quickly and for genuine interest in Citadel.

GAME Make a Market beginner~12 min Quote a tight two-sided market on a fact or a guesstimate you can't know exactly, while an interviewer tra… Pro GAME Probability Trainer intermediate~3 min Timed, freshly generated probability questions: dice, cards, conditional probability, Bayes and expected value… Pro

Practice this round 20 problems →

#1033 Quickselect: Finding the K-th Smallest Elementseen 2024-06 coding medium #1000 N-th Smallest Element in a Dynamic Streamseen 2017-06 coding medium #922 Design Tic-Tac-Toeseen 2025-06 coding medium #1032 Queue with O(1) Get-Maxseen 2023-06 coding medium #1064 Trie Prefix Search Implementationseen 2016-06 coding medium #695 Conditional Probability for Bernoulli Sumseen 2023-06 probability easy #909 Conditional Uniform Selection: Expected Valueseen 2021-06 expectation easy #906 Conditional Expectation Given an Even Functionseen 2024-06 expectation easy #908 Conditional Expectation of the Maximum Order Statisticseen 2023-06 expectation medium #376 Expected Flips for Consecutive Headsseen 2021-06 expectation medium

Behavioral / Culture-Add Round

30 min · with senior researcher Round guide →

Candidate-reported as a separate 30-minute round: 'Why Citadel' + 'tell me about a project' + 1 ethics/dilemma scenario. In the published QR and engineering processes, behavioural questions sit inside the first technical round, and engineering adds a leadership interview after the three technical interviews.

Practice this round →

Editorial round — no practice problems.

Trading / Market-Making Simulation

45–60 min · interactive · trading & QT tracks Round guide →

Trading/QT track: Citadel Securities runs live market-making simulations. Quote a two-sided market on an uncertain value as the interviewer trades against you; update quotes and inventory as flow reveals information. Scored on quote discipline, inventory awareness, and clear reasoning under pressure over exact numbers. Rehearse below.

GAME Make a Market beginner~12 min Quote a tight two-sided market on a fact or a guesstimate you can't know exactly, while an interviewer tra… Pro

Practice this round →

Super Day - Quantitative Math

60 min · whiteboard Round guide →

Part of the all-day Super Day (a series of ~45-min interviews). Two or three probability/statistics problems back-to-back - expect full derivations, not just final answers.

Practice this round 30 problems →

#7 Breaking a Stick into a Triangleseen 2025-06 probability easy #501 HTH vs HTT Pattern Raceseen 2019-06 probability medium #14 Optimal Stopping: Three-Roll Dice Gameseen 2025-06 expectation medium #15 Pirate Gameseen 2025-06 game-theory easy #25 Bugs on a Barseen 2025-06 expectation medium #90 Expected Number of Loops from Tying Rope Endsseen 2024-06 expectation medium #131 Probability No One Gets Their Own Hatseen 2023-08 probability medium #119 Optimal Sequential Rank Guessingseen 2022-06 probability hard #123 Optimal Stopping in the Red-Black Card Gameseen 2026-06 game-theory medium #476 Penney's Game with Biased Coinseen 2026-06 game-theory hard #1384 Coupon Collector With Unequal Types: Playing Cardsseen 2022-06 expectation hard #1464 Order Statistics of Exponentials and Spacing Structureseen 2024-06 random-variables hard

Super Day - Coding

60 min · CoderPad (Python preferred) Round guide →

A Super Day round: one medium-hard algorithmic question plus a practical 'clean up this messy code' refactor. C++/Python emphasis; correctness, edge cases, and complexity under time pressure.

Practice this round 24 problems →

#442 Largest Rectangle in Histogramseen 2024-06 coding hard #458 Median of Two Sorted Arraysseen 2026-06 coding hard #524 Trade-by-Trade Realized P&L Engine With FIFO Matchingseen 2023-06 coding hard #1185 Online Statistics and Sampling: Welford, Reservoir, and Alias Methodseen 2026-06 coding hard #1518 2D Fenwick Tree for Rectangle Sum Queriesseen 2022-06 coding hard #1682 Segment Tree with Lazy Propagation for Range Add and Range Minseen 2022-06 coding hard #1671 Range Minimum Query via Sparse Tableseen 2025-06 coding medium #1708 Union-Find with Path Compression and Union by Rankseen 2023-06 coding medium #1599 LFU Cacheseen 2023-06 coding hard #1605 Longest Duplicate Substringseen 2026-06 coding hard

Super Day - ML / Statistics (QR & ML roles)

60 min · whiteboard Round guide →

A Super Day round for QR/ML tracks: regression, model diagnostics, regularization. They probe assumptions hard - be ready to justify 'why does this hold.'

Practice this round 28 problems →

#902 Closed-Form Lasso Under Orthonormal Designseen 2021-06 regression medium #1066 Two-Stage Least Squares with Overidentificationseen 2017-06 regression hard #1799 Recursive Least Squares Updateseen 2023-06 regression hard #1971 GLS and Cochrane-Orcutt for AR(1) Errorsseen 2020-06 regression hard #1457 Omitted Variable Bias in OLSseen 2025-06 regression medium #1456 Omitted Variable Bias and Suppressor Variablesseen 2022-06 regression hard #1453 OLS Slope When the True Relationship Is Non-Linearseen 2023-06 regression medium #1861 Linear Regression, Ridge, and Lassoseen 2026-06 regression medium #1892 Why L1 Regularization Produces Sparse Solutionsseen 2016-06 machine-learning medium #1877 Regression with More Features Than Observationsseen 2020-06 regression medium #1718 Angle Between y and y-hat in Ridge Regressionseen 2016-06 regression hard #1893 ACF and PACF of an ARMA(1,1) Processseen 2026-06 time-series hard

Team-Fit / Final Round

45 min - with hiring team Round guide →

After the Super Day, hiring managers across Citadel and Citadel Securities review your feedback; teams that are interested run a final fit interview. For quant/research this is often one open-ended prompt ('design an alpha' / 'a paper you would actually trade'); for SWE it is a senior-engineer team match.

Practice this round →

Editorial round — no practice problems.

The day before

Re-derive the OLS β̂ + standard error formula on a napkin.
Pick one ML paper from the last 12 months you can speak to.
Drill mental math for the market-making roles (less for QR).

Cheatsheet →

Looking for other firms?

Every firm has a curated interview-questions playlist — a ready-to-drill set of problems matched to how that firm interviews, each with a full worked solution.

Practice every firm's OA: timed replicas, free game replicas and guides in one place →

Drill the Citadel / Citadel Securities practice set (97 problems) → Browse all company playlists →

Citadel round-by-round guides

Citadel interview guide: the firm, culture, roles and pay →

Stage guides for every firm: superdays · behavioral questions · market-making games

Citadel / Citadel Securities interview — FAQ

What is the Citadel / Citadel Securities interview process?

Citadel runs the largest interview funnel in the industry. QR roles emphasize ML and statistics; market-making roles (Citadel Securities) emphasize fast math, pricing, and microstructure. The funds are technically separate companies: interview structures differ slightly by business unit, but Coding + Stats are nearly universal. The loop runs 8 stages: Online Assessment, First-Round Phone Screen, Behavioral / Culture-Add Round, Trading / Market-Making Simulation, Super Day - Quantitative Math, Super Day - Coding, Super Day - ML / Statistics (QR & ML roles), Team-Fit / Final Round.

How many rounds does Citadel / Citadel Securities have?

8 stages in total, starting with the Online Assessment and ending with the Team-Fit / Final Round.

How do I prepare for the Citadel / Citadel Securities interview?

Work the stage notes above, then drill the Citadel / Citadel Securities interview-questions set and the Citadel / Citadel Securities online-assessment practice — each problem has a full worked solution.