Old Mission Capital is a Chicago proprietary trading firm founded in 2008, with further offices in New York and London. It was started by Joe Guzowski, who traded at Susquehanna and LaBranche Structured Products before founding it, and Patrick Nichols, a former Jane Street trader. The firm trades its own capital, takes no outside investment, and runs to a few hundred people rather than a few thousand.
Old Mission is an ETF market maker first. Its specialty is pricing the hardest-to-price and most illiquid ETFs and ADRs, and it acts as an authorised participant for major issuers. Options market making exists but is not the identity the way it is at SIG, Akuna or Chicago Trading Company, so preparing for this as a generic options-first process aims at the wrong target.
Being small and flat has a direct effect on the process: candidates routinely reach very senior interviewers early, in some cases the CEO, and the whole loop moves quickly.
- 1Online assessment. A HackerRank test, in two parts for trading and quant candidates.
- 2Recruiter screen. A short call, around 20 minutes, on your background and motivation.
- 3Technical interviews. One or more rounds with traders, or a systems-heavy loop for engineers.
- 4Final round. Senior leadership, sometimes a partner or the CEO.
Candidates report an unusually fast process, with roughly 18 days from application to decision and some junior trader loops closing inside a week, and consistently describe the recruiters as responsive. The exact number of rounds varies by role and by year, so treat the sequence here as typical rather than fixed.
Stage 1: Online assessment
Delivered on HackerRank for most roles, and the format splits sharply by track.
| Track | What you sit |
|---|---|
| Trading and quant | Two parts. First a tightly timed test on sequences and probability, not conceptually hard but speed-gated. Clear it and a second follows with Python and deeper probability. One recent report describes roughly 35 probability questions of increasing difficulty, from brainteasers up to numerical work, plus one standard Python problem |
| Software engineering | A coding assessment that candidates report reaching LeetCode-hard difficulty, with about an hour on the clock and no test cases provided |
How to prepare
- Arithmetic, because the first test is gated on speed rather than difficulty. Drill it on the Math Trainer until the pace stops being the problem.
- Sequences, on the Sequence Trainer, with our guide to sequence problems for the pattern families worth recognising instantly.
- Probability, at volume, since the second test is mostly this. Work the probability questions and the cards and coins collection, and use the probability and statistics course if the foundations need shoring up.
- Python, to the level of writing one clean correct solution under time. For engineering roles, practise hard problems with no test cases, so you are checking your own edge cases.
Stage 2: Recruiter screen
A short call, around 20 minutes, covering your resume, why trading, why Old Mission, work authorisation and the logistics of the rest of the process.
How to prepare
Have a specific answer for why Old Mission over its competitors alongside the standard why trading. The ETF specialty is the obvious hook and the one most candidates miss: saying something real about pricing illiquid ETFs separates you immediately from an answer that would fit any prop firm.
Stage 3: Technical interviews
One or more calls with traders, and candidates report being able to skip a round by performing well. The content diverges completely by track.
The trading and quant track
- Mental maths. Multiplying two and three digit numbers, dividing fractions, under time and out loud.
- Probability and combinatorics. Dice and card problems, conditional probability, and harder set pieces: the pirates gold-splitting problem, a Markov-chain question on a chessboard, and a geometric probability question on whether four random points on a sphere form a tetrahedron containing the centre.
- Statistics. Estimation, confidence intervals, the normal distribution and skew.
- Fermi estimation. Practise on the Fermi questions.
- Options theory. Which options or combinations to buy in a given scenario, plus basic Greeks and pricing intuition.
- Market making games. You quote a two-way market, the interviewer trades against you, and you requote each round.
A representative options question: a stock trades at $100, a three-month European call and put are both struck at $100, the call costs $6 and the put costs $4, rates are near zero and there are no dividends. Is there an arbitrage?
With rates near zero and no dividends, the right-hand side collapses to S minus K.
Here the call minus the put is $2 while the stock minus the strike is $0, so parity is violated and the call is rich against the put. Sell the call, buy the put, buy the stock, and the $2 is locked in. The question is checking that you hold parity as an equation you can act on, not as a fact you can recite.
The software engineering track
Notably lower-level than most trading-firm loops, and candidates report up to five one-hour interviews back to back. Reported ground: implementing standard library containers by hand, an unordered_map, a deque with correct iterator invalidation, an allocator, a lazy leaky singleton. Alongside that, Linux fundamentals and writing a feature for a C++ library at the command line, virtual memory, SFINAE, and competitive-programming problems at around Codeforces Div 2 D level.
The tech stack is modern C++ under tight latency constraints, so the depth expected is real rather than a proxy for general programming ability.
How to prepare
For the trading track, drill the probability questions and the option theory questions, and practise quoting out loud on the dice game with our guide to make me a market alongside it.
Given what Old Mission actually trades, the ETF Strategy Trainer is the most on-target preparation on this site for this firm specifically: fair value, premium and discount, the create and redeem arbitrage that keeps an ETF tethered to its basket, and index ratios and replication. The ETF arbitrage game puts the same ideas under a clock. Almost no candidate arrives able to talk about this, and it is the firm's entire business.
For the engineering track, implement the containers by hand rather than reading about them, and revise memory, the OS internals and templates properly.
Stage 4: Final round
A final interview with senior leadership, sometimes the head of desk or a partner, and in some reported cases the CEO. It revisits the maths and probability, adds more market making, and weighs fit.
The market making here tends to be on open-ended quantities rather than dice: one reported prompt asks you to make a market on the total number of Olympic gold medals the United States has won. The graded skills are a sensible central estimate, a width that reflects genuine uncertainty without being absurd, and disciplined updating after every fill.
How to carry the day
Move your market after each trade. If the interviewer lifts your offer, the true value is probably above it, so shift up rather than standing still and being picked off repeatedly in one direction. Explain your reasoning as you go, because the reasoning is what is being marked. And because the firm is small enough that you may be talking to a founder, treat the fit questions as real rather than a formality.
Closing remarks
Old Mission's process is math and probability heavy in the way its peers are, but two things make it its own. The assessment is front-loaded and speed-gated, so raw pace on the first test decides a lot before anyone reads your reasoning. And the firm's identity is ETFs, not options, which means the candidate who can talk credibly about pricing an illiquid ETF stands out in a field preparing for a generic market making interview.
For engineers the loop is unusually low-level: implementing containers by hand and answering on memory and OS internals is a different preparation from the algorithm grind that clears most trading-firm screens.
The trade-off candidates describe is a smaller brand and a leaner structure, set against high impact early, approachable senior people and a process that moves fast. Work through everything we have for Old Mission Capital, and read our full interview guide for how these stages compare across firms.