It looks smaller than it probably is because it's a sailboat. If it were a motor yacht, it would have at least two more decks. Imagine with masts and sails.
This is a great video that shows in detail how difficult it is to move such a giant when not under its own power!
His 127m/417ft Y721 departed Damen Verolme for Oceanco in Alblasserdam in the morning. The yacht is under construction for Jeff Bezos. Images of The Nautical Lady & Dutch Yachting.