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Citadel Securities · Software engineer · Experienced (and strong new grads)

Onsite: Systems & Low-Level Fundamentals

A spoken deep-dive on low-level fundamentals, C++-flavored given Citadel Securities' low-latency stack

What they actually ask

The question shapes this round uses. Larpy does not read these out. It builds each one from your own resume, because the generic version is the one you have already rehearsed.

  • “Explain what happens in memory when an object is created and destroyed in C++, and how you avoid leaks.”
  • “How do you reason about cache locality, and why does it matter for low-latency code?”
  • “How would you make a shared data structure thread-safe, which concurrency primitives would you use, and what are the tradeoffs?”
  • “What happens across the stack when a program reads from a network socket?”
  • “How does the OS schedule threads, and what does a context switch cost?”

What this round is judged on

  • Low-level depth · memory management, RAII, undefined behavior
  • Concurrency · thread safety, primitives, and their tradeoffs
  • Performance intuition · cache locality and why it matters for latency
  • Systems knowledge · OS scheduling, context switches, networking basics
  • Communication · precise, first-principles explanations

Where this round sits

Citadel Securities’s published process. Lime marks the stage this round runs.

  1. 01
    Application / resume screen
  2. 02
    Online assessment (OA)
  3. 03
    Technical phone screen
  4. 04
    Onsite / Superdaythis round
  5. 05
    Hiring decision / committee
What happens in each stage›
Application / resume screen
Recruiter and/or hiring-team screen of resume and background against the target level. SWE and Quant Research (QR) are distinct tracks with overlapping but different loops.
Online assessment (OA)
SWE: HackerRank (occasionally CodeSignal), typically 2-3 hard algorithmic problems, ~60-90 min, strong DS&A bar. QR: heavier probability/statistics/math plus some Python. Format and vendor vary by cycle and campus.
Technical phone screen
One live coding interview (CodePair-style shared editor), ~45-60 min, DS&A focused for SWE. QR phone screens skew to probability, statistics, brainteasers, mental math and light coding.
Onsite / Superday
Multiple back-to-back rounds. SWE commonly: the signature 'evolving problem' coding round, one or more DS&A rounds, a systems / low-level fundamentals conversation (C++ / memory / concurrency), and a behavioral / motivation round. QR: probability & statistics deep-dive, a Python/data coding round, a stats/ML modeling conversation, and a fit round.
Hiring decision / committee
Debrief and hiring decision. Bar is high; strong DS&A and clean, adaptable design are consistently emphasized.

Sources

Built from what Citadel Securities publishes about its own process and from real interview data. No leaked question lists. The questions you get are generated against your own resume, so they are not from anyone else's interview.

Sources last checked . Hiring loops change, so this date is the honest limit on everything above.

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