For everything? I was under the impression they still ran all the big stuff on their internal cloud with Borg and all the other infrastructure tooling they built.
Yeah, you should think of it more like GCP runs on Borg, not the other way around, although the description is not perfect. Also Google's cloud services like Cloud Spanner and Cloud Bigtable run directly on Borg.
What's terrifying is that Google described each of their B4 sites as having 60tbps uplinks in 2017, growing at 100x per 5 years. So a 250tbps undersea cable is nice but when you think about it probably not enough to make intercontinental transfer too cheap to meter.
My understanding is that GCP is essentially selling off extra capacity in those data centers, so for example your VM running in GCP is scheduled by Borg under the hood. So it's more like GCP runs on Google, rather than Google running on GCP.
