No, the privacy extensions simply use a random interface ID instead of deriving it from the MAC address. You still use a single /64 subnet as usual.

(Unless there is an aspect of the privacy extensions I'm not familiar with, but this is what people usually mean when they say "privacy extensions.")

As far as I know the privacy extensions only cycle through the host portion of the address (lower 64 bits) so they should work fine with just a /64. Access to a bigger prefix may help you get around systems that do IP banning in /64 chunks though.