Enterprise agent adoption varies, with some opting for managed platforms and others building custom agent hubs. Developers creating their own hubs need reliable tools for predictable execution, logging, and sandboxing. The Antigravity SDK provides a runtime engine and CLI for building these hubs, offering safety policies, telemetry, and stateful persistence. It powers a multi-agent control plane that monitors and manages LLM workloads. This control plane includes the Antigravity SDK agent core for model interactions and tool execution, and an observability layer using Lifecycle Hooks for real-time telemetry. A use case involves operations engineers monitoring multiple agents, which traditionally presents challenges like fragmented logs and lack of visibility. The Antigravity SDK offers a solution with a streaming API, lifecycle hooks, a policy engine, skills management, and session state for a unified view. Behind the scenes, the runtime handles session initialization, skill resolution, concurrent stream generation, and sandboxed tool execution. Telemetry interception through lifecycle hooks allows for real-time observation and steering of agent execution. The SDK is organized into four core building blocks: modular skills, sandboxed tools, session isolation, and real-time telemetry.