The 4th Flatiron is really 3 different slabs, between each slab is a gully or hanging garden diagonaling up and north between for hundreds of feet. Between the first and second slab it is a simple notch up top, but between the second and third slab, it is an odd grassy trench, a hanging garden of sorts.In this trench, which one would normally step down into from the second slab, then run up and Northwest to the third slab, on the North side, there is a ridge of steep puzzle pieces running a length from a large pine that grows against the rock and continues for maybe 80 feet. The ridge is jugs, sidepulls, and underclings on "puzzle piece" holds that looks like a loose-fit jigsaw puzzle the entire way to the opening of the gully. The rock is almost universally solid. The crux move is a move up and left on big holds perhaps 15' off of the deck and comes about 1/3 way through the route. If you fell, you'd probably break something and proceed to roll 50-100' down the gully through rocks, so this is a boulder problem for climbers who WILL NOT FALL. Consider it a highball.
The rating is V0 or V1. I said V1 in approach shoes, particularly considering the enduro factor of the climb.