git:20260813.14437ae to git:20260905.508e6a7

5 added, 5 removed. Audit A to A.

---

name: model-cost-compare

disable-model-invocation: true

description: "Starter: compare model costs for a described task — maps task shape to the cheapest adequate seat and shows the price spread"

---

# Model Cost Comparison (Starter Pack)

Answer "which model should I use for this, and what will it cost?" with numbers instead of vibes.

## When to use

The user describes a task (bulk refactor, deep review, quick lookup, long-context analysis) and wants the cheapest seat that is still adequate.

## Steps

1. **Classify the task.** Bucket it: mechanical (rename, format), standard coding, hard reasoning (architecture, security review), long-context (>200K tokens input), or web research.

2. **Estimate volume.** Rough input/output token estimate from the described scope (files touched × average size; state the assumption).

- 3. **Price the roster.** Using the cost table in CLAUDE.md ($/MTok input/output), compute the estimated cost for each plausible seat: Claude Opus 5 ($5/$25), Claude Sonnet 5 ($3/$15), Fable 5 ($10/$50, 1M context, opt-in), Codex GPT-5.6 Sol ($5/$30), Terra ($2.50/$15), Luna ($1/$6), Perplexity Sonar Pro ($3/$15), and the included-cost seats (agy, copilot, ollama, cursor-agent) at $0.

- 4. **Recommend one seat.** Pick the cheapest adequate option and defend it in two sentences. Mechanical work goes to included or budget seats; hard reasoning justifies Opus 5 at `high` effort; only a bounded judgment-class call (ambiguous architecture, API design, product tradeoffs) justifies Fable 5 at twice the Opus price.

- 5. **Check risk surfaces.** Regardless of the classification, escalate specifically to Opus 5 when the task touches API or schema contracts, security-sensitive code or CI configuration, release artifacts, user-facing UI, a new module, or a breaking change. Fable 5 remains limited to bounded judgment-class calls and is never the security-audit seat. Cheap-seat agreement never settles a judgment-class decision.

+ 3. **Price the roster.** Using the cost table in CLAUDE.md ($/MTok input/output), compute the estimated cost for each plausible seat: Claude Opus 5 ($5/$25), Claude Sonnet 5 ($2/$10), Fable 5.1 ($10/$50, 1M context, explicit-only), Codex GPT-5.6 Sol ($4/$20), Terra ($2/$12), Luna ($0.20/$1.20), GPT-6 Astra ($10/$50, explicit-only), Perplexity Sonar Pro ($3/$15), and the included-cost seats (agy, copilot, ollama, cursor-agent) at $0. For Astra requests above 272K input tokens, apply 2x input and 1.5x output pricing to the full request.

+ 4. **Recommend one seat.** Pick the cheapest adequate option and defend it in two sentences. Mechanical work goes to included or budget seats; hard reasoning justifies Opus 5 at `high` effort; only a bounded judgment-class call (ambiguous architecture, API design, product tradeoffs) justifies Fable 5.1 at twice the Opus price.

+ 5. **Check risk surfaces.** Regardless of the classification, escalate specifically to Opus 5 when the task touches API or schema contracts, security-sensitive code or CI configuration, release artifacts, user-facing UI, a new module, or a breaking change. Fable 5.1 remains limited to bounded judgment-class calls and is never the security-audit seat. Astra is also explicit-only and does not provide independence from GPT-5.6. Cheap-seat agreement never settles a judgment-class decision.

6. **Show the spread.** A three-row table: recommended seat, one cheaper-but-riskier option, one premium option, each with estimated dollars for this task.

## Guardrails

- - Never recommend Fable 5 or fast-mode Opus by default; both are 2x standard Opus cost and are opt-in only.

- - Never recommend Fable 5 for security audits; its safety classifiers can refuse offensive-security phrasing. Security review goes to Opus 5 (see `skills/blocks/fable5-prompting.md`).

+ - Never recommend Fable 5.1, Astra, or fast-mode Opus by default; these premium seats are opt-in only.

+ - Never recommend Fable 5.1 for security audits; its safety classifiers can refuse offensive-security phrasing. Security review goes to Opus 5 (see `skills/blocks/fable5-prompting.md`).

- If the estimate exceeds $1, say so explicitly before any dispatch happens.