As taken from: https://www.geekzone.co.nz/forums.asp?forumid=158&topicid=236018&page_no=2

What is the future of CGNAT on Bigpipe?
After we've completed our planned work, CGNAT will no longer be used on our connections. Any Bigpipe customer who has not purchased a static IPv4 address will instead obtain a dynamic, public IPv4 address after the changes have completed.