The elevator tower and stair tower have been formed (and possibly poured.. hard to tell) another level up, and the foundation walls have been wrapped in rigid insulation foam almost all the way around and covered back up with soil. There’s probably also some gravel fill and a footer drain pipe running around the base of the foundation walls as well. The concrete pads look like they’re intended to provide for structural support, and the rest of the interior space will likely be covered in rigid insulation, then poured as a slab.