The coordinator-subagent pattern: the foundation every Claude multi-agent system is built on

Agent Teams landed in Claude Opus 4.6. Everyone's excited. But before you touch experimental features, understand the foundational pattern everything is built on. TL;DR Coordinator receives task, delegates to specialists via tool calls Each subagent gets its own isolated context window and system prompt Subagents cannot talk to each other — everything routes through coordinator Same stopReason loop as single-agent, tool calls just dispatch to separate API calls 3–4x token cost vs single agent — only use when specialist quality justifies it Pattern 1 — Coordinator-subagent (pure API) The flow looks like this: User Request ↓ Coordinator Agent ←── stopReason: tool_use ↓ Route to specialist ↓ ┌──────────────────────────────────┐ │ research_agent │ writer_agent │ ← Each: isolated context, │ reviewer_agent │ any_specialist │ own system prompt, own tools └──────────────────────────────────┘ ↓ Tool result back to coordinator ↓ stopReason: end_turn → return answer Here's the full working implem