As of June 2026, the Agent Development Kit (ADK v1.0) is the recommended way to build code-first, deterministic, and autonomous workflows in Google Cloud. It fully replaces the deprecated Vertex AI Extensions.
The ADK includes native support for the Agent-to-Agent (A2A) protocol, allowing your Vertex agents to securely discover and delegate tasks to external agents across different platforms using standardized Agent Cards.
The new Interactions API (GA June 2026) provides a unified interface for managing agent session state, long-term memory, and asynchronous human-in-the-loop (HITL) handoffs.