There are much larger Ceph clusters, but they are enterprise owned and not really publicly talked about. Sadly I can’t share what I personally worked on.
Even smaller company's (< 500 employees) in today's big data collection age often have more than 1 PB of total data in their enterprise pool. Hosters like Digital Ocean hosts thousands of these companies.
I do think that Ceph will hit performance issues at that size and going into the EB range will likely require code changes.
My best guess would be that Hetzner, Digital Ocean and similar, maintain their own internal fork of Ceph and have customizations that tightly addresses their particular needs.
[1]: https://www.digitalocean.com/blog/why-we-chose-ceph-to-build...