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API Error: Content block not found means that the client could not find an expected content block. It commonly appears after a long-session resume, a tool call, or an interrupted stream.
  1. Start a new session and send only the necessary context.
  2. Update Claude Code, Codex, Cursor, or the relevant extension.
  3. Disable nonessential tool calls or experimental options temporarily.
  4. Shorten the one-shot input and avoid carrying excessive conversation history.
  5. Test the same model with one simple question.

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When to contact support

Contact support when it still happens in a new session, with a simple request, across several models, or together with an unexpected charge. Provide the Request ID, time and time zone, client and version, model, original error or screenshot, and whether all sessions or only the original session fail. Do not provide a full API key or a full conversation containing private content.