Software Engineer / Algo Engineer Interview Prep

About this loop

Hudson River Trading (HRT) is a quantitative trading firm that combines low-latency market making with longer-horizon research-driven trading. The firm is smaller than Citadel Securities or Jane Street (a few hundred engineers globally) and culturally more research-leaning, with a notable emphasis on hiring engineers who can operate across the boundary between systems engineering and quantitative research. The interview reflects this. Coding rounds skew Hard with strong emphasis on algorithmic and statistical reasoning; many problems involve probability, expected-value calculations, or applied data-manipulation problems that would plausibly fit inside a research workflow. System design rounds (more common at senior+) frequently center on problems HRT engineers actually solve: low-latency trading systems with deterministic latency budgets, market data processing across global venues, research compute infrastructure for backtesting and strategy development, real-time risk and position management. C++ dominates the low-latency paths and is the language most external candidates use in interviews; Python is widely used for research, analytics, and operational tooling. The firm splits roles roughly between Algo Developer (closer to research, works on strategies and quant infrastructure) and Core Developer (closer to systems engineering, works on trading platform and low-latency infrastructure), though the boundary is permeable and many engineers work across both. Behavioral signal exists but is lighter than at most companies; HRT cares more about whether you can think rigorously and operate in a small-team environment than about polished STAR stories.

The interview loop

1. 1
   Recruiter screen

   30 minutes. Background, level calibration, role alignment - HRT splits roles roughly between Algo Developer (closer to research, works on strategies and quant infrastructure) and Core Developer (closer to systems engineering, works on trading platform and low-latency infrastructure). Recruiters help calibrate which side fits your background.
2. 2
   Technical phone screen 1

   45-60 minutes. One coding problem at Medium-to-Hard difficulty in your language of choice - C++ and Python most common. Often includes a probability or expected-value puzzle as a warmup or follow-up. Cleanliness and explicit reasoning matter as much as the algorithm.
3. 3
   Technical phone screen 2

   45-60 minutes. Often more applied - a problem with statistical or data-manipulation flavor, or a deeper coding round in C++ for Core Developer candidates. May include a probability puzzle round of its own.
4. 4
   Onsite: coding deep dive

   60-90 minutes. Hard coding problem, often building a small system end-to-end with the interviewer asking follow-up questions about design choices, edge cases, performance, and how you'd extend the code. For Core Developer candidates, deep modern C++ knowledge expected (move semantics, RAII, allocator design, concurrency primitives, cache behavior).
5. 5
   Onsite: probability and quantitative reasoning

   60-90 minutes. Probability puzzles, often game-theoretic or multi-step. Common shapes: expected-value problems, Bayesian updating, optimal stopping, game-theoretic reasoning, statistical estimation problems. The interviewer cares more about how explicitly you state assumptions and how you reason than about whether you arrive at the textbook answer quickly.
6. 6
   Onsite: system design (senior+)

   60-90 minutes for senior and above. Trading-platform flavored. Common prompts: design a low-latency order management system with deterministic latency budgets, design market data processing across global venues, design research compute infrastructure for backtesting, design real-time risk aggregation. Depth on data layout, latency budgets, and the trading workflow expected.
7. 7
   Onsite: hiring manager / culture fit

   45-60 minutes. Conversational. Background, motivation for HRT specifically (the firm screens for this - candidates who treat HRT as 'just another trading firm' don't fit, especially given HRT's smaller and culturally distinctive engineering org), how you operate in small-team environments, examples of times you reasoned through hard technical or quantitative problems.

What Hudson River Trading actually evaluates

• →Probability and quantitative reasoning - explicit assumptions, comfort with uncertainty, willingness to reason from first principles
• →C++ depth for Core Developer roles - modern C++, RAII, move semantics, concurrency primitives, allocator design, cache behavior
• →Statistical literacy - distributions, hypothesis testing, basic ML, the kind of reasoning that fits a research-leaning trading firm
• →Low-latency systems intuition for Core Developer roles - cache lines, lock contention, kernel bypass networking, the cost model of common operations
• →Comfort in small-team environments - HRT's engineering org is smaller than at larger trading firms, and engineers operate with high autonomy
• →Genuine motivation for trading specifically and for HRT specifically - the firm hires people who actually want this domain and this culture

Topics tested

System design topics tested in this loop

Curated walkthroughs for the bounded designs that show up in Hudson River Trading's system design rounds. Capacity estimation, architecture, deep-dives, and trade-offs.

Behavioral themes tested in this loop

Sample STAR answers, common prompts, pitfalls, and follow-up strategies for the behavioral themes that decide Hudson River Trading's loop.