According to their web site at https://kairospower.com/technology/ it uses a molten fluoride salt based coolant but unlike the MSR/LFTR designs the fissionable fuel is not dissolved into the coolant; instead, the Kairos reactor design puts the fissionables in pellets that are intended to remain solid while in operation; it looks more like a pebble-bed reactor than a MSR/LFTR.