[avvt4avaw]

This is a very weird use of terminology. None of Jane Street, Millennium or Citadel are High Frequency Traders (HFTs). Jane Street is a prop trading firm who engages in market making, but is not primarily known for HFT - they are grey box (i.e. human-in-the-loop) which on the spectrum of market making strategies, is pretty much the opposite end from HFTs. Other firms in this bracket include SIG and DRW.

Millennium and Citadel are both hedge funds, who do not engage in market making at all. They are most similar to other multi-strategy hedge funds like Balyasny or Point72.

You may be thinking of Citadel Securities, who are a market making firm and do engage in high frequency trading. Other large and well known HFT firms include Hudson River Trading, Tower Research, Jump Trading, Virtu, IMC and Optiver.

[alephnerd]

I'm not a domain expert in this space, and have used HFT to refer to these firms simply due to their technical trading nature. I appreciate the explanation! The closest I've ever been to this industry was bombing an FPGA optimization interview at Citadel eons ago, but I also don't like humidity or snow for 9 months in a year, but I do like Malort and Hyde Park - such is life.

Jokes aside, I appreciate callouts and/or corrections!