The cells are layered but each cell stores 4 bits in QLC.
QLC = "Quad Level Cell", if you're like me and didn't know that.
Which is a strange name and underselling it btw, since there are 16 levels...
16 possible voltage levels, but a given memory cell can only exist in one voltage state at a time. The number of bits per cell is what actually matters, even if the names we assign to those types are dumb.
Sure, I just said that "QLC" basically implies two bits.