Jane Street has unlimited engineers and money to do this.

At least from the sidelines, it looks like they've built/forked most parts of the OCaml ecosystem to make it work (OxCaml, Dune was built by then, custom profilers, custom networking hardware, etc).

Of course a lot of their work is open source and can be used, but I wouldn't assume that it would be worth the effort to do something similar with OCaml yourself. Maybe it is! LLMs go brrr and all that.