How the agent loop works changedagent-sdk/agent-loop
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Upstream edited this page at 28 Oct 2026 18:03 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 30 Oct 2026 18:07 UTC.
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7373* **Python:** check message types with `isinstance()` against classes imported from `claude_agent_sdk` (for example, `isinstance(message, ResultMessage)`).
7474* **TypeScript:** check the `type` string field (for example, `message.type === "result"`). `AssistantMessage` and `UserMessage` wrap the raw API message in a `.message` field, so content blocks are at `message.message.content`, not `message.content`.
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76> **Example: Check message types and handle results**
76> [accordion] Example: Check message types and handle results
7777>
7878> ```python Python theme={null}
7979> import asyncio
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269269* **`PreCompact` hook:** Run custom logic before compaction occurs, for example to archive the full transcript. The hook receives a `trigger` field (`manual` or `auto`). See [hooks](https://code.claude.com/docs/en/agent-sdk/hooks.md).
270270* **Manual compaction:** Send `/compact` as a prompt string to trigger compaction on demand. Commands sent this way are ordinary SDK inputs. See [dispatch commands by name](https://code.claude.com/docs/en/agent-sdk/skills.md#dispatch-commands-by-name).
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272> **Example: Summarization instructions in CLAUDE.md**
272> [accordion] Example: Summarization instructions in CLAUDE.md
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274274> Add a section to your project's CLAUDE.md telling the compactor what to preserve. The header name isn't special; use any clear label.
275275>
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