tl;dr: AX is Google's open, declarative control plane for orchestrating agentic AI workloads, built on top of Agent Substrate. It uses Kubernetes-style YAML primitives (Tasks, Workspaces) to sandbox agents, manage networking, and checkpoint/resume idle agents in under a second—claiming to scale to billions of concurrent agent sessions per cluster. It targets a gap between stateless microservice orchestrators and batch systems, optimized for stateful, bursty agents that spend most of their time waiting on model or tool responses.