I've heard about 125 miles, which would be similar to the Monster 796 with it's similar sized tank. I would hope for slightly better MPGs, with 12 less HP, but it's producing more torque at a lower RPM so it's still burning plenty of fuel throughout the rev range.
To me, this is the biggest negative about the bike, as well as the previous generation Monster.
MCN also show an average MPG of 52. Meaning they calculate the 154 miles range as usable range with a 0.6 gallon (2,3 liter) reserve. Even better. The computer calculated range indication should make up for the missing fuel gauge. And there's a fuel low light.