it should be, although garmin in their usual lack of customer support don't tell you it's v.4 anywhere on the website.
buy it from johnny appleseed though and it's the same price plus they tell you it's v.4 at least.
you can still buy the old v.3 from dick smith for $49 though. given how out of date some parts of the topo maps are, i doubt v.4 will have much more accuracy than v.3. they rely on govt data being updated and i have a feeling v.4 won't have much more accuracy in the tricky spots.