Marcel Hirscher skis a more advanaced Slalom Technique than his competitors.
After releasing his skis from the previous turn, Hirscher has so much energy and momentum from that release, he can use this momentum to tip his feet downhill "upside down" without falling inside.
The key to his success and the same goes for Ted ligety in GS, is his total collapse of the inside leg and the relaxation of the inner half of his body. Compare to the next photo 1/8 of a second later.
The inside leg and ski are very light; therefore easy to tip toward the outside edge of that new inside ski. We call this the little toe edge side of the inside ski.
Modern skiing is about using and preparing the inside of the body correctly, rather than the old focus of previous eras on the outside leg and ski. Continuing with the inside theme, which is the most importnat part of the body to focus on to acheive angles, Hirscher flexes the inside leg to remove any pressure. He does so to allow his hips to drop further inside. (Below photo)
Also going along with the inside theme is his inside arm and hand, which he pushes forward like an outrigger, to stay ahead of his hip. This is in contrast to Felix Neureuther, who often reaches down and misses the forward push, His hand often goes back and causes unwanted rotation of the body.
The forward push accomplishes two things, It creates a counter acting of the upper body and hip; as
well as keeping the hand and arm ahead in case a saving touch on the snow is necessary.
(Photo above) With the sense that the turn is complete and the pressure is adequate on the outside ski, the revesre begins to happen for the release to the next turn. The outside leg now flexes and retracts aggressively. The inside arm and hand lead is increased to hold the LTE of the inside ski for transition, by holding counter-acting for the release. Retraction is so fast and aggressive that the old outside ski (stance ski) is lifted.
(Photo above) Now both knees have the same amount of flexing. His action is now however, focused totally on the "old" outside ski and leg, to get them tipped toward the new arc. This will become the new inside ski and leg and therefore it is the most important aspect of movement to the new arc. Both skis are light and this gives the skier easy lateral movements, as the skis are almost totally unweighted.
(Photo above) This edge change takes about 1/8 of a second. Notice how far apart his knees are relative to his feet. This is becasue he is trying to tip the new inside ski before the outside ski comes to a weighted edge. His ski is light so he can lead tipping with the inside foot which moves the knee inside. Biomechanically this is relevant as it is the inside of the body that dictates how the CG moves to the inside of the new arc. The focus is no longer on the outside of the body and ski, for turn set up, as in old school thinking. If the inside of the body doesn't move out of the way, it blocks the outside from creating angles needed at this level of skiing. Hirscher has this figured out better than anyone.
Notice how he has also moved his new inside arm and hand forward from the previous photo, this is to set up his counter acting and strong inside lead for the next arc.
The dynamics of modern day skiing are based in movements that create angles quickly and efficiently. Many will be unware and confused about this change in skiing, but only these movements will move a skier closer to world class technique.