They use CoTS LPDDR memory chips running at the same JEDEC timings as everyone else. Yes, they glue these chips to an interposer board like a GPU with HBM, but

They use CoTS LPDDR memory chips running at the same JEDEC timings as everyone else. Yes, they glue these chips to an interposer board like a GPU with HBM, but unlike those GPUs they aren't doing it for any performance requirements. Keeping it on package just makes things more compact so they can shrink the motherboard even more.