IIUC agent-sandbox and agent-substrate (the one ax builds upon) are similar. Agent-sandbox is more k8s-native, while agent-substrate is less so.

Personally I think that this kind of workload is better off not being tied too much into kubernetes. I've worked with crossplane and other controller who put a lot of load on the k8s-apiserver and etcd and can easily slow the whole machinery down / grind them to a halt.

btw, agent-substrate is in the process of being moved to CNCF: https://github.com/cncf/sandbox/issues/523