I’ve been curious, but I really need a better up-close shot at the switch-mode controller (not that square attiny44) to tell for sure. It’s that chip between the U3 label and the LED- wire.
I think it’s a FET-driven turbo with all other modes being buck (or buck-boost) driven for constant current. I’m positive about the buck (or buck-boost) bit, I’m just not 100% sure on how Turbo is driven. If you check out the runtime graphs in my review at 1lumen.com you’ll see that in the first 30 seconds or so, output kinda sags like what seems typical of FET-driven behavior. It then goes into temperature-controlled ramp down, then in very stable regulated output.