Put Fable 5.1 to Work Checking Opus 5.5: Claude Code's Advisor, Set Up With One Prompt
Claude Code's /advisor lets Opus 5.5 keep doing the work while Fable 5.1 reads the whole session and steps in at the moments that matter, for less than running Fable all the time. How it works, what it costs, and one prompt that sets it all up.
If you run Claude Code on Opus 5.5 and you have Fable 5.1, Fable is probably sitting there doing nothing. You either pay for it on every turn or you don't use it at all. Claude Code's advisor tool is the middle road: Opus keeps doing the work, and Fable gets called in to check it at the moments where a mistake would cost you.
It fits long jobs where most turns are routine but the plan decides the outcome: a big refactor, a bug that keeps coming back, anything you'd want checked before Claude calls it done.
How the advisor works
- Opus stays your main model and does everything: it reads the files, writes the code, runs the commands.
- At the moments that matter, Claude calls the advisor in. It tends to be before committing to an approach, when the same error keeps coming back, and before saying a task is done. Claude decides when; it isn't on a timer.
- The advisor gets the whole conversation, every tool call and every result, not a summary.
- It sends back guidance and never touches a tool itself. Opus applies it, and pushes back if a file or a failing step contradicts the advice.
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