r/crackquanttrading

More and more members of my community are reporting being asked to design complex systems in quant dev interviews.

This isn’t the classic “Design YouTube”, or “Design a Webcrawler”, it’s “Design a pro-rata orderbook with LMM behavior”.

And instead of just talking through it, they’re being asked to implement it with working code in a longer-than-average interview round.

Note: I’ll add this problem to getcracked.io, it was asked by IMC.

Likewise, I remember personally getting a “Design a low-latency communication protocol” by Belvedere, which I will be making a Youtube video on shortly (another community member got asked the same problem at Optiver).

This is more of a PSA than it is a post containing the educational material I usually like to share.

I am curious if you’ve been asked any notable system design questions that you’d like to share.

There was a quant meltdown in 2007 which was caused by a ton of quant funds who ran almost identical math-based stock strategies absolutely killed it for years… until one big unwind triggered a chain reaction, funds dropped 20–40% in days because everything was too crowded. Fast-forward to now (2025–2026) and the warning lights are flashing again. Similar story, massive inflows into quant strategies in 2025, too many funds chasing the same edge.

For the past 2 years quantitative strategies alone have captured more than 70% of the industries $78-$116 billion in net inflows, 2025 being the strongest calendar year SINCE 2007, hedge funds as a whole pulled in $115.8 billion in net inflows that year. 2007 was also a record inflow year for quant hedge funds seeing an inflow of roughly $194 billion industry wide. 2025 saw a "quant wobble" where systematic long-short equity quant funds lost about 4.2% on average, so are we really learning from our mistakes?

I do understand that the absolute dollar inflows in 2025 were a bit lower than the 2007's peak, but the concentration into quant strategies is even more extreme. The industry is also larger today ($5T vs $2T back then).

Andrew Lo's Adaptive Markets Hypothesis does explain it well, he sees financial markets like a jungle, trading strategies aren't fixed rules, they're living "species" of behavior that compete for limited resources. They adapt, reproduce (get copied), and die when the environment changes. When the ability to adapt fails, reproduction becomes a ticking time bomb on resources, therefore looking at these things top-down to imagine the environmental change that is required to cause the meltdown (death) can give us heaps of insight.

Scarcity is value. When everyone does the same thing, markets fail.

I remember when I wanted to be an investment banker back in University.

I had a long beard, long hair, and definitely did not fit in with the Brads of the world.

Their parents were partners at Morgan Stanley. Mine?

Immigrants. A working father and a stay-at-home mother.

I stood no chance.

I didn't fit the mold, and didn't want to either.

So what did I do instead? I networked.

I took classes after school taught pro-bono by a former investment banking partner professor, Blair Robertson.

Guess who the class was made up of?

All immigrant brown and Asian kids looking to break into a space that their parents didn't already dominate.

Brad? Yeah, he was too busy partying to attend. He'd already secured his internship at Lazard that summer through his parents.

But passion wasn't enough. I had to intellectually mog Brad too if I wanted to stand a chance.

So I attended the National Investment Banking Competition (NIBC). It was a conference of over 30 teams from 30 schools around the world held in Toronto.

Over a three day period my team went from last to first. I spoke infront of partners from the world's top banks infront of 500 students with under 12 hours of preparation. We each won $2000 CAD, what seemed like a fortune at the time.

What came of it? Nothing. Any internships? Nope. Interviews? Nope. Phone calls? One.

>You know, it's pretty late in the recruiting cycle. You can always try next year!

Ha... Next year? Yeah, no thanks.

I'm not interested in trying to be someone else for another year.

I networked, I studied, I competed, and it wasn't enough, simply because I wasn't already connected. So how does all this relate to quantitative trading?

Quant = 1 / Investment Banking

While passion never mattered in investment banking, it mattered tremendously in quant.

While intelligence never mattered in investment banking (any monkey can build a DCF), it mattered tremendously in quant.

Networking is probably the least important in the hierarchy of needs in quantitative trading. Whereas it's a fast-path into investment banking.

Don't get me wrong, a referral is useful, especially as you become more senior. But everyone whose already in the industry has the ability to network their way into a referral. Whereas not everyone is privilaged to be born into a connected family.

But that privilage does not matter in quant. Your competance, pedigree, and ability to perform is far more important than who your father is.

I filmed a video yesterday going over the Purdue CS240 drama.

In short, 70% of the class was caught dead-to-rights with regards to cheating.

That means 90% of the class cheated, but the professor was 110% sure that 70% cheated (and not-so-certain about the others).

Unfortunately for these students, most will graduate without knowing how to convert a string to an integer (manually). In fact, even before AI, 50% of students that graduated from Guelph (a Canadian university), according to my friend, couldn't do so.

What does that mean for someone grinding for quant based on first-principles?

It means that, as your colleagues are taking the quick-and-easy path, the ROI of grinding has never been higher.

Even if they cheat their way to the on-site. they won't pass the whiteboard / in-person coding round.

This should be exciting news for anyone looking to break into the space.

In fact, when I was interviewing for CTC back in the day, simple implementing a threadsafe SPSC queue with a consumption policy (non-type template parameter) had the interviewer saying "You're a breath of fresh air".

Knowing your sh*t has never been more advantageous.

I've recently seen posts from people claiming to use cheating software to cheat their way into Jane Street.

They've been shared in my community, and the stories sound believable.

I want to stress that these are most likely fake. In fact, the accounts that post them end up getting suspended a couple of hours later (Reddit is really on it).

Quant firms have several interview rounds, many of which require on-site live coding, where you don't have access to AI or other cheating software.

At my previous firm, we made the candidate go through two rounds of live coding. One where they needed to solve a problem alone, in an isolated room, where snacks and water would be delivered to them.

Another one where they had to code and debug live with the Head of Engineering, and one other developer. They had to walk through their reasoning and defend the choices they made.

I've had interviews where I needed to code on a whiteboard, and even on paper. Yes, on paper!

Quant firms don't play, and if they're going to pay you total compensation (TC) of upwards of 300K, you better come correct; they'll make sure of it.

A member of my community shared this reddit post from r/cpp_questions.

It's a user who is shocked and bewildered that HFTs actually ask nuanced questions about the details of C++, concurrency, and systems in interviews.

This is something I've been hammering as important for months, ever since I started my call-in show (which I plan to get back to).

Unfortunately, there are three groups of detractors as it relates to 'TrIviA'.

1. People who have never interviewed for Quant, and think it's FAANG (those that don't know any better).
2. People who do know that this is how Quant interview, but feel as though the bar is too high (those that do know better).
3. People that know that this is how Quant interview, but would rather cope in not knowing the answer to the question than step back and ask 'Where do I go to learn this?'.

The poster, in this case, belongs to group 1. Group 1 is the most honest group; they're naive (in the kindest sense of the term) and simply are caught off-guard.

These are the people getcracked is best suited for. They're open-minded, willing to learn, and simply hit a patch in the road. Maybe the patch caused a flat tire, but they can be up and running in no-time.

90% of people end up in the third bucket. They know (deep down) that these questions are asked in Quant, but would rather attack the messenger than deal with the contents of the message (the question). Or worse, they want to attack getcracked's credibility by claiming it 'only tests trivia', despite the trove of coding questions, roadmaps, quizzes, interview games, and soon-to-be video content.

It's very hard to break through to these people.

Well, now that the developer ecosystem is starting to wake up, hopefully we can move away from this aweful term 'trivia'.

There is nothing 'trivia'-like about knowing the inner-workings of a language you will be using day-to-day.

There is nothing 'trivia'-like about information you will need to excel at your job in.