# Claude Fable 5.1 vs Claude Opus 5

> Markdown mirror of https://router.one/models/compare/claude-fable-5-1-vs-claude-opus-5 for AI assistants and crawlers. Router One is an OpenAI-compatible LLM API gateway.

Claude Opus 5 is the lower-priced of the two on Router One — about 72% less on a 1M-input + 1M-output mix. Both carry a 1.05M context window. Both answer on /v1/chat/completions and /v1/messages (Claude Code).

Claude Fable 5.1 and Claude Opus 5 compared on current per-token rates, context window, and capabilities — both callable through one OpenAI-compatible endpoint with per-request cost traces.

## Claude Fable 5.1 vs Claude Opus 5: rates, context window, and capabilities

| Spec | Claude Fable 5.1 | Claude Opus 5 |
| --- | --- | --- |
| Input / 1M tokens | $8.00 | $2.25 |
| Output / 1M tokens | $40.00 | $11.25 |
| Cached input / 1M tokens | $0.80 | $0.375 |
| Context window | 1.05M | 1.05M |
| Detail page | [Claude Fable 5.1](https://router.one/models/claude-fable-5-1) | [Claude Opus 5](https://router.one/models/claude-opus-5) |

## What does 1M tokens cost on Claude Fable 5.1 vs Claude Opus 5?

For a workload of 1M input plus 1M output tokens at current rates: Claude Fable 5.1 comes to $48.00, Claude Opus 5 comes to $13.50 — Claude Opus 5 is about 72% cheaper on this mix. Real workloads skew heavily toward input tokens, so weigh the input rate by your own ratio; the cached-input row above is the posted catalog rate for that model.

## Switch between Claude Fable 5.1 and Claude Opus 5 without changing code

Both models are behind the same OpenAI-compatible endpoint, so an A/B test is a one-string change — same key, same code, and every request traced with tokens, cost, and latency in the dashboard:

`compare.sh`

```bash
curl https://api.router.one/v1/chat/completions \
  -H "Authorization: Bearer sk-your-router-one-key" \
  -H "Content-Type: application/json" \
  -d '{"model": "anthropic/claude-fable-5.1", "messages": [{"role": "user", "content": "Hello"}]}'

# Same request, other model — change one string:
#   "model": "anthropic/claude-opus-5"
```

## FAQ

### Is Claude Fable 5.1 cheaper than Claude Opus 5?

Input: Claude Fable 5.1 $8.00 vs Claude Opus 5 $2.25 / 1M tokens; Claude Opus 5 has the lower rate. Output: Claude Fable 5.1 $40.00 vs Claude Opus 5 $11.25 / 1M tokens; Claude Opus 5 has the lower rate. Total cost depends on the workload's input, output and cache usage. Rates change; the /models page is the live source of truth.

### Can I switch between Claude Fable 5.1 and Claude Opus 5 without changing code?

Yes. Both are served through the same OpenAI-compatible endpoint, so switching is changing the model string in the request — the key, base URL, and request shape stay identical.

### Where do these numbers come from?

Specs and prices on this page render from the live Router One catalog — the same data as the /models page — and refresh with it. Pricing methodology is documented on /pricing-methodology. Rates on this page were read from the live catalog on 2026-09-07 (UTC) and refresh within the hour.

## More comparisons

- [Claude Opus 5 vs GPT-5.6 Sol](https://router.one/models/compare/claude-opus-5-vs-gpt-5-6-sol)
- [GPT-6 Astra vs Claude Opus 5](https://router.one/models/compare/gpt-6-astra-vs-claude-opus-5)
- [Claude Opus 5 vs Claude Opus 4.8](https://router.one/models/compare/claude-opus-5-vs-claude-opus-4-8)
- [Claude Fable 5 vs Claude Opus 5](https://router.one/models/compare/claude-fable-5-vs-claude-opus-5)

## See also

- Canonical page: https://router.one/models/compare/claude-fable-5-1-vs-claude-opus-5
- All model comparisons: https://router.one/models/compare
- All models & prices: https://router.one/models (markdown: https://router.one/models.md)
- Pricing: https://router.one/pricing
- Claude API access: https://router.one/cheap-claude-api
- Cost calculator: https://router.one/llm-cost-calculator
- Pricing methodology: https://router.one/pricing-methodology