VPCs and subnets now support more sizes for IPv6 CIDRs

Amazon VPC allows customers to create VPCs and subnets of different sizes using IPv6 CIDRs. With this capability, customers can now create VPCs in sizes between /44 and /60, and subnets in sizes between /44 and /64, in increments of /4. Before today, AWS supported one standard IPv6 CIDR block size of /56 for VPC and /64 for subnet, whereas IPv4 CIDR block size were flexible for both VPCs and subnets.

Source:: Amazon AWS