It's compass' own Rat Trap, a massive 2.3 slick (54mm) that weight a mere 418g for the extra light version.
That's only slightly heavier than my Grand Bois Hetres (412g), which show the main advantage of the 26" being able to stay light at such a large sizes.
@edscoble Any ideas what the tyres on Jan's firefly is? I'm running 26" btw and liking the look of them.