I covered that. Edge routers transition 1.x.x.x.x to x.x.x.x as a default, and x.x.x.x to 1.x.x.x.x. This is an interim change, so that ipv4 can communicate to ipv4 forever. Legacy systems can be supported on ipv4 only, relegating them (just as they are now!) to not having access to that new address space.