I want a Google App Engine service (GAE Java 17 Runtime) to have a static outbound IPv4 so that 3rd party services can whitelist that IPv4 in their firewall.
At the same time this service needs to access IPv6-only resources.

According to this a static outbound IP in GAE can be achived via Serverless VPC Access and Cloud NAT. In my understanding the architecture looks like this:

It works for IPv4 as described in the documentation and all outbound communication are correctly showing the public IP of the NAT. However, no IPv6 resources can be accessed via this setup.

This is stated as a limitation of Serverless VPC Access (“IPv6 traffic is not supported”). It seems that the VPC itself supports dual-stack and probably IPv4 traffic and IPv6 traffic could be routed separately through the network, so that only IPv4 goes through the NAT. But the Connector from GAE to the VPC is the issue here.

Without the NAT the service can access both IPv4 and IPv6 resources, but the outbound IP is not static. So it seems you have to choose between dual-stack capabilities and static IP.

Question: What options are there to support static outbound IP dual-stack in GAE?