The fundamental concept is a vehicle traveling in a vacuum tube. Making this a high vacuum tube is too much of a joke for even Ol' Musky to suggest, so the consensus is that these hyperloop-family devices use low vacuum just because it's more feasible. Air resistance is only one major source of friction though, the other is the friction between the car and the track. The air bearing idea, which is to essentially fit the car and the track together with tightly toleranced metal and pump a small amount of high pressure air in the gap to keep the rail and the car isolated, is a viable way of getting a low friction interface, but for various reasons magnetic levitation, where the train and the track are isolated by magnetic or supermagnetic forces, has kind of rendered it obsolete afaik (also, maglev and air bearings are mutually exclusive unless they're doing something really weird).