And, as it turns out, the original recommendation to go with /48s turned out to be insufficiently flexible, and was overridden with https://tools.ietf.org/html/

And, as it turns out, the original recommendation to go with /48s turned out to be insufficiently flexible, and was overridden with https://tools.ietf.org/html/rfc6177 https://tools.ietf.org/html/rfc6177. In particular, some ISPs will hand out a /56 - allowing the home user 256 /64s. But, once again, these are administrative routing decisions - on the interface, it's always a /64 or (in some rare cases - though I'd love to hear if people still see this in the wild) /127s for router-router connections. You will never, ever see, for example, a /72 IPv6 network in the wild.