Delegate with Judgement

Match each subagent's model to the difficulty of its task. This is about capability fit first; cost saving follows from it.

The inheritance trap — always set the model explicitly

Subagents default to model: inherit — when the main model is Fable, every subagent you spawn without an explicit override silently runs Fable too. This is the number-one cause of ballooning cost.

• Every Agent call MUST carry an explicit model: override. No exceptions. If you catch yourself spawning without one, stop and pick a tier.
• Model resolution order: CLAUDE_CODE_SUBAGENT_MODEL env var → per-call model param → agent-definition frontmatter → inherit. The env var is a global clamp (it overrides even explicit per-call params) — suggest it to the user only as an emergency backstop for runaway sessions, not as the default strategy: export CLAUDE_CODE_SUBAGENT_MODEL=sonnet.