What is the fastest ocean deep current? The Gulf Stream is the fastest ocean current in the world with peak
velocities near 2m/s.
Source: marine.coastal.edu

What about deep currents, North Atlantic Deep Water, Antarctic Bottom Water, etc?
What is the fastest ocean deep current?
My guess is Antarctic Bottom Water must be the fastest because Antarctic Circumpolar Current receives not salty water from ice melt, and salinity gradient moves deep currents.
Is Antarctica Bottom Water the fastest?
This article in Fox News points to this paper and asserts that the fastest deep current measured is the Antarctic.

Rintoul, of the Antarctic Climate and Ecosystems Cooperative Research
Center in Hobart, said it proved to be the fastest deep ocean current
yet found, with an average speed of 7.9 inches a second (0.20 m/s).

I have no access to the paper, I can only read the abstract. I guess Fox News didn't lie this time as they are sourcing a scientifical paper of Nature Geoscience.
Fukamachi, Y., Rintoul, S., Church, J. et al. Strong export of Antarctic Bottom Water east of the Kerguelen plateau. Nature Geosci 3, 327–331 (2010). https://doi.org/10.1038/ngeo842