OCI now supports the use of multiple IPv6 prefixes within a VCN and subnet, and IPv6 addresses from different prefixes can be assigned to a VNIC. You can choose between receiving a /56 GUA prefix allocated from Oracle, assigning a prefix from a range you own and have imported via the BYOIP verification process, or specify a ULA prefix.

You may assign 3 total IPv6 prefixes per VCN and subnet, and assign IPv6 addresses from up to 3 prefixes to a VNIC.  Up to one Oracle-allocated GUA prefix may be assigned to each VCN and any combination up to 3 total GUA (Oracle-allocated 1 or BYOIPv6 GUAs) or ULA prefixes may be assigned to the VCN. 

Documentation for this support is in Overview of VCNs and Subnets, IPv6 Addresses, and Bring Your Own IP.