I've seen a lot of posts asking about this. None is clear to me. Comcast seems to want you to pay for IPV4 addresses. With trillions of IPV6 addresses, it makes no sense to charge for them if they are.
Comcast supplies dual stack (IPv4 and IPv6) public / WAN IP addresses to your connection. They do not charge extra for your public IPv4 IP address. You would only pay extra if you wanted additional public IP addresses assigned to your connection. And this is not even available in all market areas.