Most cables are privately owned, as is most of the internet actually. The telcos juts interface with each other and sell each other bandwidth on their cables.

Most cables are privately owned, as is most of the internet actually. The telcos juts interface with each other and sell each other bandwidth on their cables. That said, Google will likely reserve some portion of the cable for their inter-datacenter use. That’s how you get fast cross region data transfer in GCP. Same for AWS and Azure, all have some capacity reserved for data between their datacenters.