Comment by reincarnate0x14

You can do the exact same thing in V6 if you want, there are so many extra bits you can have DHCPv6 or assigned addresses pack all kinds of things in there. With ULAs there are 16-bits for network ID, which is so sparse you can type the VLAN ID in decimal and ignore that you're losing the overhead. People will often put in joke address like deadbeef that can be fit into hex (the 40-bit global ID should be random but for hobbyist purposes most people are willing to suffer re-numbering it in the unlikely event their homelab is bought out by IBM). If you'd rather eat into the interface id portion, you can technically do whatever you want in there although packing too much in may locally cause problems in some routers if you try to treat it like additional network id bits. It's the equivalent to have both middle bytes of 10.x.y.z available for whatever while still having a few hundred billion available subnets.

Just as an example google's public DNS is 2001:4860:4860::8888 because their v4 dns is 8.8.8.8.