advisor-tool changedagents-and-tools/tool-use/advisor-tool
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341341| `advisor_redacted_result` | `encrypted_content`, `stop_reason` | The advisor model returns encrypted output. |
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343343<Note>
344 Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5, Claude Fable 5, and Claude Mythos 5 advisors return the encrypted `advisor_redacted_result`. Every other advisor model in the [compatibility table](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) returns the plaintext `advisor_result`. To read the advice text in your own responses, use an advisor that returns plaintext, such as `claude-opus-4-8`, where your executor's row in the [compatibility table](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) lists one. Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5, Claude Fable 5, and Claude Mythos 5 executors pair only with advisors that return the encrypted form, so on those executors the advice text isn't readable in the response.
344 Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5.5, Claude Opus 5, Claude Fable 5, and Claude Mythos 5 advisors return the encrypted `advisor_redacted_result`. Every other advisor model in the [compatibility table](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) returns the plaintext `advisor_result`. To read the advice text in your own responses, use an advisor that returns plaintext, such as `claude-opus-4-8`, where your executor's row in the [compatibility table](https://platform.claude.com/docs/en/agents-and-tools/tool-use/advisor-tool#model-compatibility) lists one. Claude Fable 5.1, Claude Mythos 5.1, Claude Opus 5.5, Claude Opus 5, Claude Fable 5, and Claude Mythos 5 executors pair only with advisors that return the encrypted form, so on those executors the advice text isn't readable in the response.
345345</Note>
346346
347347Here is the same request sent twice, identical except for the advisor `model` in the tool definition, showing both variants.
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12361236The plain-text nudge is highly salient on Haiku and Sonnet executors: 74 percent (Sonnet) to 98 percent (Haiku) of nudged attempts in Anthropic's testing called the advisor immediately at turn 2. If that lands before your executor has read the problem or gathered context, the resulting advisor call is low-context and can displace a better-timed later call. Measure your executor's baseline first-call turn before adding the nudge. If the executor already calls the advisor reliably and its first call typically lands at turn N, set `NUDGE_TURN` greater than N. In Anthropic's testing, a turn-2 nudge on workloads where the baseline first call was turn 7 or later correlated with a 3 to 4 percentage-point task-performance drop. On a browse workload where the baseline call rate was 86 percent, the same nudge raised engagement with no task-performance cost.
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1238To force a consult on a specific request instead of nudging, set `tool_choice` to `{"type": "tool", "name": "advisor"}`, subject to the constraints in [Forcing tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/define-tools#forcing-tool-use). Forcing tool use cannot be combined with manual extended thinking (`thinking: {type: "enabled"}`): the API returns a `400 invalid_request_error` if you enable both. Adaptive thinking supports forced tool use. Claude Fable 5.1 and Claude Mythos 5.1 executors reject `tool_choice` types `tool` and `any`, so use the prompt nudge on those models instead.
1238To force a consult on a specific request instead of nudging, set `tool_choice` to `{"type": "tool", "name": "advisor"}`, subject to the constraints in [Forcing tool use](https://platform.claude.com/docs/en/agents-and-tools/tool-use/define-tools#forcing-tool-use). Forcing tool use cannot be combined with manual extended thinking (`thinking: {type: "enabled"}`): the API returns a `400 invalid_request_error` if you enable both. Adaptive thinking supports forced tool use. Claude Opus 5.5, Claude Fable 5.1, and Claude Mythos 5.1 executors reject `tool_choice` types `tool` and `any`, so use the prompt nudge on those models instead.
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12401240## Streaming
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18081808The executor model (the top-level `model` field) and the advisor model (the `model` field inside the tool definition) must form a valid pair. The advisor must be Claude Sonnet 4.6 or a more capable model, and it must be at least as capable as the executor. Models of equal capability (for example, Claude Opus 4.7 and Claude Opus 4.8) can advise each other.
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1810| Executor models | Advisor models |
1811| ------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
1812| Claude Haiku 4.5 (claude-haiku-4-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) Claude Sonnet 4.6 (claude-sonnet-4-6) |
1813| Claude Sonnet 4.6 (claude-sonnet-4-6) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) Claude Sonnet 4.6 (claude-sonnet-4-6) |
1814| Claude Sonnet 5 (claude-sonnet-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Sonnet 5 (claude-sonnet-5) |
1815| Claude Opus 4.6 (claude-opus-4-6) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) |
1816| Claude Opus 4.7 (claude-opus-4-7) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) |
1817| Claude Opus 4.8 (claude-opus-4-8) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) |
1818| Claude Opus 5 (claude-opus-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) |
1819| Claude Fable 5 (claude-fable-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) |
1820| Claude Mythos 5 (claude-mythos-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5 (claude-opus-5) |
1821| Claude Fable 5.1 (claude-fable-5-1) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) |
1822| Claude Mythos 5.1 (claude-mythos-5-1) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) |
1810| Executor models | Advisor models |
1811| ------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
1812| Claude Haiku 4.5 (claude-haiku-4-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) Claude Sonnet 4.6 (claude-sonnet-4-6) |
1813| Claude Sonnet 4.6 (claude-sonnet-4-6) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) Claude Sonnet 4.6 (claude-sonnet-4-6) |
1814| Claude Sonnet 5 (claude-sonnet-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Sonnet 5 (claude-sonnet-5) |
1815| Claude Opus 4.6 (claude-opus-4-6) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) Claude Opus 4.6 (claude-opus-4-6) Claude Sonnet 5 (claude-sonnet-5) |
1816| Claude Opus 4.7 (claude-opus-4-7) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) |
1817| Claude Opus 4.8 (claude-opus-4-8) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) Claude Opus 4.8 (claude-opus-4-8) Claude Opus 4.7 (claude-opus-4-7) |
1818| Claude Opus 5 (claude-opus-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) |
1819| Claude Opus 5.5 (claude-opus-5-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) |
1820| Claude Fable 5 (claude-fable-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) |
1821| Claude Mythos 5 (claude-mythos-5) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) Claude Mythos 5 (claude-mythos-5) Claude Fable 5 (claude-fable-5) Claude Opus 5.5 (claude-opus-5-5) Claude Opus 5 (claude-opus-5) |
1822| Claude Fable 5.1 (claude-fable-5-1) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) |
1823| Claude Mythos 5.1 (claude-mythos-5-1) | Claude Mythos 5.1 (claude-mythos-5-1) Claude Fable 5.1 (claude-fable-5-1) |
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18241825If you request an invalid pair, the API returns a `400 invalid_request_error` naming the unsupported combination.
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