Fable 5 Optimizer

Claude Code guidance for routing work across Claude Opus 5, Claude Fable 5, and Codex/GPT-5.6 Sol.

The default has changed: Opus 5 is now the everyday Claude Code lead for complex, mergeable work. Fable 5 is the escalation tier for the hardest capability and judgment gaps. Codex is a frontier peer for independent review, context gathering, alternative execution, and runtime verification—not merely a cheap mechanical worker.

The project ships as an on-demand Claude Code skill plus an optional lightweight CLAUDE.md policy.

What You Get

• A routing matrix for choosing Opus, Fable, or Codex by the actual bottleneck.
• Effort guidance that starts Opus and Fable at high and raises effort only when the task warrants it.
• Cross-model patterns that prefer one capable owner and add reviewers only for a distinct job.
• A compact context-packet pattern for state that is genuinely scattered.
• Current Codex CLI templates for read-only review, bounded implementation, and browser/computer-use verification.
• Workspace-limited safety defaults for agentic execution.

Install

Mode	Pick this if
On-demand skill (default)	You want routing guidance loaded only when a task mentions these models or asks who should own the work. Installs per user and works across projects.
Project-local skill	You want the same on-demand behavior in one repository.
Always-on router	You want a short routing policy active in every session. This also installs the detailed project-local skill so Claude can load the mechanics only when needed.

On-Demand Skill

Ask Claude Code:

install this skill https://github.com/nyldn/fable5-optimizer

Or install from the shell:

curl -fsSL https://raw.githubusercontent.com/nyldn/fable5-optimizer/main/install.sh | bash

From a cloned copy:

./install.sh

The default install writes to ~/.claude/skills/fable5-optimizer. A changed skill folder is backed up to ~/.claude/skill-backups/ first, a sibling of the skills root rather than a folder inside it, so Claude Code never discovers the backup as a second skill with the same name. Project-local installs use .claude/skill-backups/ in the project. Reinstalling an unchanged version does nothing and leaves no backup.

For a project-local install:

curl -fsSL https://raw.githubusercontent.com/nyldn/fable5-optimizer/main/install.sh | bash -s -- skill-project

Always-On Router

Run from the target project root:

curl -fsSL https://raw.githubusercontent.com/nyldn/fable5-optimizer/main/install.sh | bash -s -- claude-md

Or from a cloned copy:

./install.sh claude-md

This mode:

1. installs the detailed skill to .claude/skills/fable5-optimizer/
2. writes a managed routing block to .claude/CLAUDE.md

The managed block is intentionally lightweight. Re-running the installer replaces the block rather than stacking copies, preserves unrelated project instructions, and backs up existing files first. When nothing would change, the rerun is a byte-for-byte no-op and writes no backup.

Markers are matched as whole lines, so prose that merely mentions them is left alone. If a file opens a managed block without closing it, the installer refuses rather than guessing where the block ends. A symlinked CLAUDE.md is written through, so a dotfiles-managed file keeps its indirection. CLAUDE.md is written with your umask default.

Default Routing

Work	Start with
Complex coding, planning, debugging, review, or enterprise workflows	Opus 5
Highest-capability judgment, unusually ambiguous architecture, or a problem Opus cannot resolve	Fable 5
Independent technical review, context scouting, alternative implementation, or runtime automation	Codex/GPT-5.6 Sol
Routine or high-volume work	The cheapest capable model already in context

Use the table as a starting point, not a guarantee. For repeated workflows, evaluate models on your actual prompts, artifacts, acceptance criteria, total task cost, and rework.

Usage Examples

/fable5-optimizer should Opus own this migration, or does it need Fable?
/fable5-optimizer have GPT-5.6 Sol independently review this Opus implementation
/fable5-optimizer prepare a compact context packet before escalating this architecture decision
/fable5-optimizer verify the running checkout flow with Codex browser automation

Claude Code can also load the skill automatically when a request is about Opus/Fable/Codex routing, effort selection, cross-model orchestration, or local runtime verification.

Requirements

• Claude Code with skills support.
• Codex CLI, installed and authenticated, for Codex delegation.

Check both:

claude --version
codex --version

Without Codex, the Claude routing guidance still works.

Design Basis

The current policy is grounded in:

• Anthropic's Claude model selection guide
• Anthropic's Opus 5 prompting guide
• Anthropic's Claude 5 context-engineering guidance
• Anthropic's Claude Code skills guide
• OpenAI's reasoning-model guidance
• OpenAI's Codex sandbox documentation

Provider pricing, retention rules, model behavior, and subscription limits change quickly. Verify current terms before making compliance or procurement decisions.

Versioning

Releases follow semantic versioning and are tagged vX.Y.Z. History lives in CHANGELOG.md.

Contributing

Keep changes focused on routing policy. Put invocation-only detail under skills/fable5-optimizer/references/ so the always-loaded context stays small.

See CONTRIBUTING.md.

License

MIT. See LICENSE.