When I was involved about a year ago, cilium falls apart at around a few thousand nodes.

One of the main issues of cilium is that the bpf maps scale with the number of nodes/pods in the cluster, so you get exponential memory growth as you add more nodes with the cilium agent on them. https://docs.cilium.io/en/stable/operations/performance/scal...

Thats true and I definitely had to "tune" the bpf map limits, but it wasn't really that difficult to do.

Wouldn't that be quadratic rather than exponential?