Sort of, the google3 monorepo is so large that all checkouts are sparse checkouts. So you have a virtual checkout of everything but specify the subset you actually need.

Once you have the tooling to do this you can use the monorepo to store all kinds of interesting things, like built artifacts or the contents of the CDN, since it's basically just a giant hierarchical KV store with a global version.

Yes. And if you improve something used by both of them and have to refactor across the source tree you can do that in a single commit.

https://cacm.acm.org/magazines/2016/7/204032-why-google-stor...

yes