AFAIK they’re like a hedge fund with quants that trades its own money. In fact, most people (everyone?) who works there is a quant. It’s the only way they trade. They are extremely profitable. Of course you can Google this and get a more accurate picture. I know them as the most famous OCaml shop.

Personally I have mixed feelings about what they do. The engineer in me used to root for them. The way they operate as a pure tech shop was very refreshing in the hedge fund/traditional finance world (crypto world is the opposite). But the trader in me now abhors how they make their money, that is arguably at the expense of retail traders.