Why it matters

Hooks provide extensibility without modification. Understanding shapes agent customization.

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The architecture

Callback registration: attach to Runner or Agent.

Hook types: pre-turn, post-turn, pre-tool, post-tool, pre-LLM, post-LLM.

Lifecycle hooksRegister callbackson Runner or AgentHooks fireat lifecycle pointsCustom logiclogs, checks, modsSimilar to Spring interceptors or middleware in web frameworks
Hook mechanics.
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How it works end to end

Common uses: cross-cutting concerns (logging, metrics), authentication + authz, rate limiting per user, feature flags per session, A/B testing.

Order matters: multiple hooks execute in registration order.

Can modify: hooks can transform inputs/outputs.