The advisor tool is experimental and requires Claude Code v2.1.98 or later with the Anthropic API. It is not available on Amazon Bedrock, Google Vertex AI, or Microsoft Foundry. Behavior, pricing, and availability may change.
When to use the advisor
The advisor fits long, multi-step tasks where most turns are routine but plan quality determines the outcome. Examples include large refactors, debugging sessions where an error keeps recurring, and tasks you want independently checked before Claude declares them done.
It adds less value on short tasks where there is little to plan, or on work where every turn needs the strongest model. For those, switch the main model instead, or see how the advisor compares with opusplan and subagents for other ways to get a second opinion.
Enable the advisor
You can set the advisor model in three ways:
/advisor command: set or change the advisor mid-session and save it as your defaultadvisorModel setting: configure a persistent default in your settings file--advisor flag: set the advisor for a single session at launch
If any of these sets an advisor model, the advisor is enabled for sessions whose main model supports it. To stop using it, see Turn the advisor off.
To use Fable 5 as the advisor, you need Claude Code v2.1.170 or later and Fable 5 access for your organization. Fable does not appear in the picker that /advisor opens, so pass it directly as /advisor fable, --advisor fable, or "advisorModel": "fable". Use the /advisor command
Run /advisor without arguments to open a picker listing the available advisor models, or pass the model directly:
Your selection is saved to advisorModel in your user settings and persists across sessions. If your current main model does not support the advisor, the selection is still saved and activates when you switch to a compatible main model with /model.
Set advisorModel in settings
To configure the advisor as a default without opening a session, set it in your settings file:
{
"advisorModel": "opus"
}
Use the --advisor flag
To set the advisor for a single session without changing your saved setting, launch with the flag:
The flag takes precedence over the advisorModel setting for that session. Unlike /advisor, which saves an inactive selection, the flag exits with an error if the session’s main model does not support the advisor.
Choose an advisor model
The advisor must be at least as capable as the main model. The accepted advisors for each main model are:
| Main model | Accepted advisors | Notes |
|---|
| Haiku 4.5 | Fable, Opus, Sonnet | Haiku can call the advisor but cannot act as one |
| Sonnet 4.6 | Fable, Opus, Sonnet | |
| Opus 4.6 or later | Fable, Opus at or above the main model’s version | An Opus 4.7 main with an Opus 4.6 advisor is rejected |
| Fable 5 (v2.1.170+) | Fable | An Opus or Sonnet advisor is rejected |
fable option does not appear in the /advisor picker.
Set the advisor as opus, sonnet, or fable. These aliases resolve to the latest version of each model. You can also pass a full model ID such as claude-opus-4-8.
The API enforces the pairing, not Claude Code. Setting a rejected pairing succeeds, then surfaces as a cannot be used as an advisor when the request model is error on the next request.
Common model pairings
Any accepted pairing works. These combinations balance cost against capability in different ways:
| Pairing | When to use |
|---|
| Sonnet main + Opus advisor | Sonnet handles routine work and escalates planning, ambiguous failures, and completion checks to Opus |
| Sonnet main + Fable advisor | Fable 5 guidance at decision points without running Fable 5 throughout. Requires v2.1.170 or later and Fable 5 access |
| Haiku main + Opus advisor | Lowest-cost main model with strong planning. Expect higher cost than Haiku alone but lower than switching the main model to Sonnet or Opus |
| Opus main + Opus advisor | A second Opus reviews the first. Useful for high-stakes tasks where an independent check matters more than cost |
| Fable main + Fable advisor | Highest-capability pairing when Fable 5 is available (v2.1.170+). Fable is a higher tier than Opus and Sonnet, so it is the only accepted advisor for a Fable main model |
| Sonnet main + Sonnet advisor | A lower-cost second opinion for catching routine oversights |
When Claude consults the advisor
Claude decides when to call the advisor. It tends to consult before committing to an approach, when an error keeps recurring, and before declaring a task done, but the timing is model-driven rather than rule-based.
You can ask for a consultation in your prompt the same way you would request any tool, for example consult the advisor before you continue. There is no setting to cap or force advisor calls; if you want Claude to consult more or less often during a task, say so in your instructions.
What you see during a session
When Claude calls the advisor, the transcript shows an Advising line with the advisor model name while the call is in progress. When the result returns, the line confirms that the advisor has reviewed the conversation. Press Ctrl+O to expand it and read the advisor’s full guidance.
Claude generally follows the advisor’s guidance, but adapts when its own evidence contradicts a specific claim: if a recommended step fails when tried, or the file contents contradict the advice, Claude surfaces the conflict rather than following the guidance unconditionally.
The advisor always receives the full conversation, and Claude controls the timing. For more control or a different configuration, see how the advisor compares with subagents and opusplan.
Cost
Each advisor call sends the conversation to the advisor model, so it consumes tokens at the advisor model’s rates in addition to your main model’s usage. With API billing, advisor tokens are charged at the advisor model’s input and output rates. On subscription plans, advisor usage counts toward your plan’s usage limits.
Claude calls the advisor at decision points rather than on every turn, so pairing a faster main model with a stronger advisor typically costs less than running the stronger model throughout. Advisor usage counts toward the session totals shown by /usage.
For how advisor tokens are reported in API responses, see Usage and billing in the Claude API documentation.
Impact on prompt caching
Enabling or disabling the advisor mid-session does not invalidate your main model’s prompt cache. Unlike changing model or effort level, toggling /advisor keeps the cached prefix intact, and the advisor’s returned guidance is cached as part of the transcript on later turns.
The advisor model’s own read of the conversation is not cached. Each advisor call processes the full transcript anew, with no reuse between calls.
Requirements
The advisor tool requires all of the following:
- Claude Code v2.1.98 or later: run
claude update to upgrade.
- Anthropic API only: the advisor is a server-executed tool. It is not available on Amazon Bedrock, Google Vertex AI, or Microsoft Foundry. Through an LLM gateway configured with
ANTHROPIC_BASE_URL, availability depends on whether the gateway forwards the request intact to the Anthropic API.
- Supported main model: Opus 4.6 or later, Sonnet 4.6, or Haiku 4.5. Fable 5 also qualifies on Claude Code v2.1.170 or later.
Turn the advisor off
To stop using the advisor and clear your saved advisorModel, run /advisor off or choose No advisor in the /advisor picker:
To disable the advisor tool entirely, including the /advisor command and the --advisor flag, set CLAUDE_CODE_DISABLE_ADVISOR_TOOL=1. See Environment variables.
The advisor is one of several ways to combine model strengths. Pick based on when you want a second model involved.
| Approach | When the stronger model runs | How it starts |
|---|
| Advisor tool | At decision points mid-task | Claude calls it when it needs guidance |
opusplan | During plan mode, then switches to Sonnet for execution | You enter plan mode |
Subagents with model set | For the entire delegated subtask | Claude delegates, or you invoke the subagent |
/model | For all subsequent turns | You switch models |
See also
