fable5-optimizer

name

fable5-optimizer

description

Load before answering whenever a request mentions Claude Opus 5, Claude Fable 5, GPT-5.6 Sol, Codex, or asks which model or agent should plan, implement, review, research, or verify work. Use for model routing, cross-model workflows, Codex delegation, effort selection, context preparation, and runtime/browser verification. Do not use for ordinary implementation or review with no model-choice question, or for generic prompt rewriting.

Fable 5 Optimizer

Route work across Claude Opus 5, Claude Fable 5, and Codex/GPT-5.6 Sol without turning every task into a multi-model ceremony.

Default Policy

Start complex Claude Code work with Opus 5 at high effort. It is the everyday default for planning, production implementation, debugging, code review, knowledge work, and agentic tool use.

Escalate to Fable 5 when the task needs Anthropic's highest available capability: unusually ambiguous architecture, the hardest long-horizon work, deep or obscure knowledge, or a judgment call where Opus has exposed a real capability gap.

Use Codex/GPT-5.6 Sol as a frontier peer when an independent perspective, a different tool harness, large-context evidence gathering, persistent execution, or browser/computer-use automation is useful. It is not limited to throwaway scripts, and its output is evidence rather than authority.

Prefer one capable model end to end when that is enough. Add another model only when it has a distinct job.

Model Roles

Model	Default role	Reach for it when	Watch for
Opus 5	Everyday Claude Code lead	Complex coding, planning, refactors, enterprise work, visual tasks, review, and multi-step execution	Over-verification, scope expansion, verbose narration, unnecessary subagents
Fable 5	Capability escalation	Highest-stakes judgment, novel or deeply ambiguous problems, hardest long-running agents, obscure knowledge	Cost, latency, safety-classifier fallbacks, and data-retention constraints
GPT-5.6 Sol through Codex	Independent frontier executor and reviewer	Fresh-context review, technical edge cases, research/context scouting, tool-heavy execution, runtime verification	Broad diffs if the boundary is vague; destructive risk when the execution environment is too permissive

These are routing heuristics, not personality guarantees. Model behavior varies by harness, effort, tools, and task. For repeated work, compare models on the user's real prompts and acceptance criteria.

Routing Gate

Route by the bottleneck:

Work type	Start with
Routine lookup, classification, or small rewrite	The cheapest capable model already in context
Production coding, debugging, refactoring, code review, or business workflow	Opus 5
Architecture, product judgment, API design, UX taste, or user-facing copy	Opus 5; escalate to Fable 5 when ambiguity or stakes justify it
Highest-capability research or a problem Opus has failed to resolve	Fable 5
Independent code review, edge-case search, context gathering, or alternative implementation	Codex/GPT-5.6 Sol, then the primary Claude session verifies
Browser, app, simulator, screenshot, or computer-use verification	Whichever harness has the best local automation; Codex is often a strong route
Deterministic bulk edits or data processing	The cheapest capable execution model; Codex is often suitable

Treat API/schema contracts, security-sensitive work, release artifacts, destructive migrations, and user-facing UI as risk surfaces. Keep final judgment in the primary Claude session and escalate to Fable when the unresolved risk is genuinely capability- or judgment-bound.

Effort Discipline

• Opus 5: start at high. Use low or medium when evals show quality holds; use xhigh for demanding coding or agentic work. Do not default to max.
• Fable 5: start at high; use xhigh only for the most capability-sensitive work and lower effort for routine tasks.
• GPT-5.6 Sol: start with the Codex default. Increase effort only when the task needs deeper planning or analysis and the extra latency and token use are justified.

Effort is a tuning knob, not a substitute for a clear task or a way to extend run duration. Compare total task cost, latency, context use, tool calls, and rework—not token sticker prices alone.

Context And Handoffs

Before a cross-model handoff, state:

• the exact task and intended outcome
• relevant files, diff, artifact, or runtime target
• checkable acceptance criteria
• scope boundaries and actions that require approval
• known decisions, gaps, and validation already run

Use active context when it already contains the state. When state is scattered across files, diffs, screenshots, or prior decisions, have Codex assemble a compact context packet before an expensive judgment pass. Keep it to roughly a page: ask, current state, evidence, decisions, gaps, and the exact judgment requested.

Do not create a packet for a small task or repeat facts the receiving model can cheaply inspect.

Multi-Model Patterns

Default: one capable owner

Let Opus 5 plan, implement, and verify the task. This is the right path for most mergeable work.

High-stakes split

Use only the stages that add value:

1. Opus 5 produces the plan or implementation.
2. Codex reviews from fresh context for concrete bugs, edge cases, and missing verification.
3. Fable 5 reviews only the remaining architecture, taste, or capability-sensitive question.
4. The primary Claude session verifies findings against the artifact and resolves conflicts.

Do not require all three models for every task. Reciprocal reviews are useful for calibrating a new model or resolving real disagreement, not as a standing ritual.

Context scout

Codex can gather repository state, relevant source material, logs, and test evidence. Ask for a factual packet, not a decision disguised as a summary. The judgment model should receive sources and acceptance criteria without the maker's preferred conclusion.

Prompt Discipline For Claude 5

• Give the goal, why it matters, constraints, and output contract. For implementation, provide the complete specification up front.
• Keep instructions brief and avoid repeating the same rule across CLAUDE.md, skills, prompts, and tool descriptions.
• Let the model use judgment for routine choices. Constrain scope when different interpretations would materially change the work.
• Opus 5 already self-corrects and verifies. Remove blanket "double-check everything" steps or mandatory verifier subagents unless the workflow has a specific independent-verification need.
• State desired response or document length explicitly; effort controls thinking, not visible verbosity.
• For long-document analysis, place the source material before the question. When factual precision matters, ask for relevant extracts and ground the analysis in them.
• Do not ask a model to reveal or reproduce hidden reasoning. Ask for conclusions, evidence, tradeoffs, or a concise rationale.
• Remove legacy anti-laziness prompts, token countdowns, aggressive all-caps triggers, and micromanaged step lists.

Safety And Data Boundaries

• Use a read-only sandbox for review and evidence gathering.
• For edits, prefer a workspace-limited sandbox. Expand writable roots only to named targets.
• Do not use full-device access as the default. Require user authority for destructive, irreversible, account-changing, or externally consequential actions.
• Isolate parallel implementers in separate worktrees.
• Data governance overrides capability routing. Verify current provider retention and compliance terms before sending restricted data; do not infer them from model quality or subscription access.

Codex Workflows

Read references/codex-workflows.md only when actually invoking Codex, creating a Codex wrapper, or checking the CLI command patterns. It contains the shared report contract plus review, implementation, runtime-verification, and workflow-wrapper templates.

Reporting

Lead with the outcome. Say which model handled which distinct job, cite concrete files/checks/evidence, and identify anything not verified. If another model found no issues, name the reviewed target and report that result plainly.