Agent Substrate, an open-source agent execution runtime, is now available on Google Kubernetes Engine (GKE). This technology is designed for running millions of sandboxed autonomous agents with significantly higher density than standard containers. Agent Substrate boasts rapid suspend and resume operations, achieved through a native zero-trust kernel and network isolation. Leading AI teams, like Nous Research behind the top-ranked Hermes Agent, are already leveraging Agent Substrate. Scaling agent platforms presents challenges such as opaque trust boundaries and tool access friction. Traditional architectures struggle with massive bursts of agent activity and idle compute resources. Agent Substrate addresses these issues by decoupling agent execution from machine management. It offers security by default using microVMs or gVisor sandboxes, along with granular network controls. The system ensures sub-second activation of agents and high efficiency by suspending idle agents to free up compute. It runs on any Kubernetes cluster and is optimized for GKE, utilizing custom ComputeClasses and Arm-based processors for cost-effectiveness. Agent Substrate provides a scalable and reliable foundation for building production agent applications.