Google ADK ParallelAgent: Fan-Out/Fan-In with Output Key Isolation

Google ADK Documentation·high signal

Google's Agent Development Kit (ADK) provides a ParallelAgent primitive that calls run_async() on all sub-agents concurrently, with each agent writing results to a unique output_key in shared session state to prevent race conditions. The canonical production pattern is a SequentialAgent → ParallelAgent → LlmAgent topology: parallel branches independently gather data, then a synthesis agent merges results after all branches complete. This non-LLM-powered workflow agent eliminates sequential bottlenecks for multi-source retrieval and heavy computation workloads.