Google's open-source toolkit (ADK) for building and deploying multi-agent systems.
The Agent Development Kit (ADK) is Google's open-source framework for building, evaluating, and deploying agents, with first-class support for multi-agent hierarchies, workflow agents (sequential, parallel, loop), streaming, and tools. It powers agents inside Google's Agent Engine on Vertex AI and interoperates via the Agent2Agent (A2A) protocol.
Open-source (Apache 2.0). Free to use; hosted deployment on Vertex AI Agent Engine is billed by Google Cloud usage.