thinking-troubleshooting changedbuild-with-claude/thinking-troubleshooting
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14 Aug 2026
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123123The message says thinking is disabled because `between_tools` has no up-front thinking. With `between_tools`, effort can't change mid-conversation: a per-message `output_config.effort` that differs from the level in effect returns a 400 error. `messages.N` is the position of the message that set the new level.
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125Claude Haiku 5.5 returns the same message for a per-message effort change while `thinking: {type: "disabled"}` is set.
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127Remove that per-message effort, or set it to the level in effect. To vary effort per turn, use adaptive thinking, which is what the message means by "enable thinking".
125Remove that per-message effort, or set it to the level in effect. To vary effort per turn, use adaptive thinking: omit the `thinking` field or send `thinking: {"type": "adaptive"}`. That's what the message means by "enable thinking".
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129127Claude Haiku 5.5 returns the same message when a request with `thinking: {type: "disabled"}` sets a per-message effort that differs from the level in effect. Remove that per-message effort, or set `thinking` to `{"type": "adaptive"}` to vary effort per turn.
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