VM interfaces are assigned IP addresses from the subnet that they are connected to. Each VM interface has one primary internal IPv4 address, which is assigned from the subnet’s primary IPv4 range. If the subnet has an internal IPv6 range, the VM interface can optionally be configured with an internal IPv6 address.
https://cloud.google.com/compute/docs/ip-addresses#:~:text=VM%20interfaces%20are%20assigned%20IP,with%20an%20internal%20IPv6%20address.