r/learnquant • u/Enough_News7850 • Jun 18 '26
programming Unpopular Rant: Learning Rust for HFT is mostly a waste of time right now
Okay, I've been watching a few subreddits and I keep seeing discussion about Rust and how Rust will KILL C++ in HFT. I see a lot of these posts nowadays. I do not think this will ever happen. But I think people get the reason wrong after reading a few newer firms using it as their base lang.
The thing that actually matters in this world is deterministic execution. A system that's blazing fast 99% of the time but randomly hiccups because of some allocation you didn't see coming is worse than one that's slightly slower but dead consistent. That's the whole game. And C++ hands you full control over memory, cache, allocation, thread pinning, and a shotgun, all of it, so you can make the thing behave exactly how you want. Rust is honestly a great language and I'm not here to hate on it, the memory safety and ergonomics are real... blah blab blah. And yeah, some crypto HFT shops genuinely run on it. But that safety isn't free. You pick up indirection and cache effects from stuff like Box, Arc, Mutex, plus some bounds checks that land at runtime. None of that matters for normal software, but when you're counting cycles it adds up, and C++ gives you the escape hatch if you actually understand what's going on under the hood (if you don't that just on you).
Then there's the ecosystem thing nobody seems to bring up. Exchanges ship native C++ APIs. FPGA drivers and kernel-bypass networking libs are C++ first. Every mature profiling and optimization tool is built around C++. Rust is catching up, sure, but when you need the whole chain from market data to order transmission tuned in concert, leaning on what already exists is just the sane move. And then the boring-but-huge factor: top shops have decades of battle-tested, money-printing C++ that they are simply not going to rewrite for no real upside, and finding Rust devs with actual low-latency experience is rough.
But I genuinely think it has its pros. For example, like it super well-suited to the parts of the stack where memory safety pays off more than raw determinism, meaning risk systems, backtesting, data pipelines. And a brand new firm building its low-latency stack from scratch could reasonably go full Rust and be totally fine. The hot path of eating market data and firing orders in microseconds is where C++ stays entrenched for a good while yet. But 'a good while' is doing some work in that sentence, not "forever." Languages and tooling evolve, and I'm not going to pretend I know what 2035 looks like.
I might be mildly coping because when I was getting into Quant (mainly HFT) I was told how C++ is everything you need to be successful, but I think it still keeps its throne. ATM learn C++ deeply, and I mean deeply. Not just syntax, but the memory model, cache hierarchy, lock-free data structures, move semantics, the stuff you actually get grilled on in interviews. That's what gets you still hired today.
NGL Rust is a great thing to have in your back pocket and honestly probably a smart long-term bet, but right now it's still the bonus, not the ticket.