VPC peering in-out data transfer when the traffic is within the same Availability Zone

Based on the information available, you should not be charged for VPC peering data transfer that stays within the same Availability Zone (AZ).

AWS announced a pricing change for VPC peering where "all data transfer over a VPC Peering connection that stays within an Availability Zone (AZ) is now free." This includes both IPv4 and IPv6 traffic since VPC Peering supports both protocols.

There might be some confusion due to the general pricing rules that state IPv6 data transferred between different VPCs is charged at $0.01/GB in each direction. However, this general rule is superseded by the specific VPC peering pricing policy for same-AZ traffic.

If you're seeing charges for VPC peering traffic within the same AZ, it could be due to:

1. The traffic might actually be crossing AZs
2. You might be using public/elastic IP addresses for communication between instances rather than private IPs
3. There might be a billing error

It's worth noting that while same-AZ VPC peering traffic is free, inter-AZ data transfer typically incurs charges. Similarly, AWS has made inter-AZ data transfer free for certain services like AWS Transit Gateway, AWS PrivateLink, and AWS Client VPN, but this may not apply to all services.
Sources
IPv6 VPC peering cost clarifications | AWS re:Post
Data Transfer Charges | AWS re:Post
Questions about Data trasnfer charge ** | AWS re:Post