A subagent is a focused specialist that a main agent (the orchestrator) or a human sends to do one defined piece of a larger job and report back. The boundary is the point: a subagent needs its task, the files it may inspect, the output format, and where to stop. The context window is a big reason subagents exist. Large work fills context fast, so a subagent can handle a bounded task and bring back a clean summary while the main agent keeps room to make decisions.
Imagine a general contractor and subcontractors. You don’t hire one person to hang drywall, wire the house, pour concrete, and plumb it all personally. The contractor coordinates, the electrician handles wiring, the plumber handles plumbing. Each has a tighter lane.
Why you care
Used well, you still talk only to the lead: you define the outcome, the lead routes the pieces, and you review the finished work. That’s delegation routing. More subagents means more delegation, which only helps when the pieces are clear and someone owns integrating the results. Complex work improves when the right specialist handles the right piece.