I can confirm this, no brake lights even at 4 chevron regen. The regen brake level without the brake being pressed is well below the threshold where it would be legally required.I tested this out at night time while going downhill (I can see the brake lights refected off the stop signs & street signs behind me when they turn on). When I let go of the gas pedal the brake lights DO NOT turn on at full regen. It only turns on when the brakes are pressed.
However, ACC will activate the brakes. Driving down steeper hills or if it slows for a vehicle it is following the brakes might illuminate.