The funny thing with k8s is that Google doesn't use it (except GKE, and there's a reason it's one cluster per customer).

Their internal tooling scales just fine, but all it shares with k8s is some of the underlying concepts. Unlike, say, Bazel, gVisor or Gerrit, which are the real thing (minus some secret sauce tied to internal infra). k8s is good software, and best-in-class when it comes to open source options, but the idea that it is "open source Borg" is silly.