# Cc Model Routing > Model Routing - Skill: `lobbi-docs/cc-model-routing` (Agent Skill) - Install (CLI): `npx skillmds@latest add lobbi-docs/cc-model-routing` - Raw SKILL.md: https://api.skillmd.com/api/skills/lobbi-docs/cc-model-routing/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: AI & ML - Author: Lobbi-Docs (https://skillmd.com/u/lobbi-docs) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/lobbi-docs/cc-model-routing --- # Model Routing Claude model choice is the biggest cost lever in Claude Code. Match the model to the work. ## Decision matrix | Task type | Model | Why | |---|---|---| | Long-horizon autonomous run (overnight build, large migration end-to-end) | Fable | Sustains multi-hour agentic work and async subagent fleets that stall lesser models | | Hardest unsolved problem (Opus failed or would need many retries) | Fable | Highest reasoning ceiling; one Fable pass can beat several Opus retries | | Architecture decision | Opus | Multi-step reasoning; hidden-cost detection | | Root-cause debugging (hard) | Opus | Hypothesis trees, multi-source evidence | | Security review | Opus | Risk sensitivity; knowledge of OWASP/CWE | | Feature implementation | Sonnet | Standard generation; good reasoning | | Code review (routine PR) | Sonnet | Fast; catches most issues | | Test writing | Sonnet | Pattern-based | | Research / docs lookup | Haiku | Fast; cheap; sufficient for retrieval | | Bulk file edits (rename, reformat) | Haiku | Mechanical work | | Dependency audit | Haiku | Running commands, parsing output | | Simple Q&A | Haiku | One-shot factual answers | ## Cost table (approximate, check `cc_docs_model_recommend` for current) | Model | Alias / ID | Input $/M | Output $/M | Relative | |---|---|---|---|---| | Fable 5 | `fable` / `claude-fable-5` | $10 | $50 | 3.3× | | Opus 4.8 | `opus` / `claude-opus-4-8` | $5 | $25 | 1.7× | | Sonnet 5 | `sonnet` / `claude-sonnet-5` | $3 | $15 | 1× | | Haiku 4.5 | `haiku` / `claude-haiku-4-5-20251001` | $1 | $5 | 0.33× | Output tokens are the dominant cost in most Claude Code sessions. Two caveats on Fable 5: its new tokenizer produces ~30% more tokens for the same content (so the effective gap vs Opus is wider than the per-token price), and turns run longer. Use it where the capability ceiling matters, not as a default. Sonnet 5 uses the same new tokenizer (~30% more tokens than Sonnet 4.6 for identical content) and launched with introductory pricing ($2/$10 per MTok through 2026-08-31) — the table shows the sticker price. **Aliases auto-resolve to the latest generation** — prefer `fable`/`opus`/`sonnet`/`haiku` over pinned IDs so a model refresh doesn't strand your config. Use `opusplan` for Opus-reasoning + Sonnet-execution, or `best` for "most capable available". Extended 1M-token context: `opus[1m]` / `sonnet[1m]` (Fable 5 is 1M by default; `claude-fable-5[1m]` is the long-context ID form). **Fast mode** (`/fast` in-session, `--fast` at launch) keeps you on Opus (4.6/4.7/4.8) but optimizes for faster output — it does **not** downgrade to a smaller model. Toggle it when you want Opus-level reasoning without the usual latency. Not available on Fable 5. **Effort levels** scale reasoning depth independently of model: `low` · `medium` · `high` · `xhigh` · `max` (Opus 4.7/4.8, Sonnet 5, and Fable 5 support `xhigh`). Set via `/effort`, `--effort `, or `effort:` in skill/agent frontmatter — cheaper than jumping a model tier when you just need deeper thinking. On Fable 5 thinking is always on and effort is the *only* depth control — and even `low` effort on Fable often matches or beats `max` on prior models, so sweep downward for routine work. ## Model cascading The high-leverage pattern: start with a cheap model for planning, delegate implementation to cheap, reserve Opus for review gates. | Phase | Model | |---|---| | Plan mode (Shift+Tab) | Opus (Fable for the hardest/longest-horizon plans) | | Implementation | Sonnet | | Subagent research | Haiku | | Code review gate | Opus | | Final sign-off | Opus | | Overnight / multi-hour autonomous run | Fable (orchestrator only; workers stay on Sonnet) | Net effect: most tokens are on Sonnet/Haiku; Opus tokens are where they matter most; Fable tokens are reserved for the rare runs that justify the tier. ## Budget planning For a task estimated at N turns: - Rough floor: 2k input + 2k output per turn = 4k tokens. - Sonnet cost: 4k × $3/M = $0.012 per turn. - 20-turn session on Sonnet: ~$0.24. - Add 3 Opus review passes: +$0.45. - Total: ~$0.70. Use `cc_docs_model_recommend(task, budget)` to get a specific recommendation with cost projection. ## Downgrade/upgrade triggers **Downgrade to Haiku when**: - Doing pure retrieval (grep results, file reads). - Running a known command and parsing output. - Rate-limited on Sonnet budget. **Upgrade to Opus when**: - Sonnet gets it wrong twice on the same subtask. - Task is security-critical. - Stakeholder cost of error is ≥ days of engineer time. - You're designing something new (vs. implementing something known). **Upgrade to Fable when**: - Opus has failed (or would clearly need multiple retries) on the same problem. - The run is long-horizon and autonomous — overnight builds, end-to-end migrations, multi-wave orchestration where mid-run drift is the failure mode. - You're coordinating a fleet of long-lived async subagents and need the orchestrator to stay coherent for hours. - Don't route security-scanning/offensive-security analysis to Fable — its cyber safety classifiers can refuse (`refusal` stop reason); keep that on Opus. ## /plan mode `Shift+Tab` toggles plan mode — uses Opus to think deeper without producing code. Use for: - New feature scoping - Debugging a tough bug before trying fixes - Architecture choice before committing Don't use plan mode for: known patterns, mechanical work, small tweaks. ## MCP delegation | Need | Tool | |---|---| | Model recommendation for a task | `cc_docs_model_recommend(task, budget?)` | | Compare two model choices | `cc_docs_compare(["opus", "sonnet"])` | | Check cost of an autonomy profile | `cc_kb_autonomy_profile(profile)` | ## Anti-patterns - Defaulting to Opus everywhere → ~1.7× cost, rarely 1.7× value on routine work. - Defaulting to Fable everywhere → 3.3× price *and* ~30% more tokens per task; the tier pays off only above Opus's ceiling. - Haiku on hard tasks → gets it wrong, then you re-run on Opus = wasted double cost. - Ignoring `/plan` on new work → code-first on unfamiliar problems wastes tokens. - Not estimating budget → costs creep; you notice on the monthly bill.