SonicOS provides the default network address object, Pref64 to support the NAT64 feature.
It is the original destination for a NAT64 policy and is always pref64::/n. You can create an address object of Network type to represent all addresses with pref64::/n to represent all IPv6 clients that can do NAT64. Refer to the below screen shot as an example.
A well-known prefix, 64:ff9b::/96, is auto created by SonicOS. For more information about Pref64, refer to: