HFT firms would likely use the exchange binary protocols where available over FIX. Ie: OUCH/ITCH, Pillar etc. With that said, FIX is still relevant on many exc

HFT firms would likely use the exchange binary protocols where available over FIX. Ie: OUCH/ITCH, Pillar etc. With that said, FIX is still relevant on many exchanges and in wide use by the broker/dealers etc...