I've been confused about this, and I just want to be certain of what it is before I attempt a run.
@Khazixstann All runs in 2-Island%, 4-Island% and All Squads% are played on Easy. You can see what difficulty they are being played on by looking in the top right corner right as the run is about to start. I'm not 100% sure about All Squads%, but it would not surprise me that it's Easy for that as well. I would assume 100% is also played on Easy, but I cannot be certain due to the fact that I'm not as certain about certain achievements in this game. There is a Hard-Mode category is Misc. runs that require runs to be played on Hard.
All Squads is played on Easy, All Achievements does multiple runs, most of them on Easy whenever possible, some of them on Hard when it is needed for achievements