My CLAUDE.md Model Routing section — Fable orchestrates, gpt-5.5/Opus execute (+ the codex-runner wrapper agent it references)

Fable has implemented a model routing system in its CLAUDE.md file that prioritizes intelligence and taste over cost. The system delegates bulk mechanical work to gpt-5.5 via Codex CLI, while user-facing tasks requiring taste are handled by Claude (Fable/Opus tier). A codex-runner wrapper agent is used to invoke gpt-5.5 within Claude workflows.

You have standing permission to route work to the best model without asking. Judge the output, not the price tag — if a cheaper model's output doesn't meet the bar, rerun or redo the work with a smarter model without asking. Escalating costs less than shipping mediocre work. Priority order: intelligence taste cost. Cost is a tie-breaker only. "Taste" covers UI/UX, code quality, API design, and copy. Routing defaults not limits — override when the output demands it : Bulk/mechanical work clear-spec implementation, data analysis, migrations, mechanical refactors : delegate to gpt-5.5 via the Codex CLI ~/.codex/config.toml defaults to gpt-5.5 at xhigh effort . For investigation/analysis that shouldn't touch files, run codex exec -s read-only directly with a self-contained prompt. User-facing work UI, copy, API design — anything needing taste : keep on Claude Fable/Opus tier . Reviews of plans/implementations : get a cross-model second opinion before shipping significant work — /codex-audit for deep code audits, /codex-iterative-v2 for iterative plan review, /codex-debate for A-vs-B decisions. Browser-based UI verification / computer use : prefer delegating to Codex — currently stronger there. Revisit this assumption as models change. Claude subagents/workflows : set the model param deliberately — sonnet for mechanical stages, opus/fable for judgment-heavy stages reviews, synthesis, design . Haiku only for trivial lookups, never for anything that ships. gpt-5.5 inside Workflows or the Agent tool the model param only takes Claude models : spawn the codex-runner agent agentType: 'codex-runner' , effort low — a thin wrapper that shells out to codex exec and returns the result.