Fan-out / fan-in is a concurrency pattern commonly used in agentic orchestration. In the fan-out phase, an orchestrator decomposes a task into independent subtasks and dispatches them to separate agents or workers in parallel. In the fan-in phase, it collects all results, merges or reconciles them, and produces a unified output. This pattern dramatically reduces wall-clock time for parallelizable work — such as searching multiple sources, running independent analyses, or processing document batches — at the cost of increased coordination complexity.