The Haiku XP-G is essentially the same light as the Haiku with the exception of hosting a Cree XP-G based Light Engine coupled with a new McR-17XP reflector designed speciffically for the LED and application. Both use the 3S converter for three levels of output.
A comparison of the Haiku and Haiku XP-G:
The XP-G LED has a larger die than the XR-E and although it can't be driven at as high a current, it boasts greater flux at lower drive levels, relative to the XR-E.
Bead Blasted version on 2xAA battery pak:
Recent addition to the Haiku line is a Haiku XM-L using the Cree XM-L LED: