OCaml is used by Jane Street but no one else in this space (certainly no major player). Jane Street are a successful and respectable company but no giant, by any standard. If anything, I'd say their fame for using OCaml is greater than their fame as a trading firm.
The benchmark would need to be Java or C++, which are the mainstay of the industry.
I actually sort of suspect that the most common reason for people to have heard of Jane Street is their advertising for internships on maths related YouTube channels. (Not the most common reason for their customers or partners, just the greatest number of people)
Thanks I appreciate the info. I love python and I use it for nearly everything. But it often gets dogged for perf, so I wonder about the reasoning in using it for high frequency trading despite the bad rap.
1) even before the speedups done now on CPython, PyPy has always existed (and NumPy was HW-accelerated)
and more importantly 2) It has a native arbitrary-precision decimal type. Even other languages seriously used in financial institutions like OCaml (https://discuss.ocaml.org/t/ocaml-needs-an-arbitrary-precisi...) doesn't even provide it natively.