# Claude Fable 5.2 vs Claude Opus 5.5

> Markdown mirror of https://router.one/models/compare/claude-fable-5-2-vs-claude-opus-5-5 for AI assistants and crawlers. Router One is a unified, OpenAI-compatible LLM API gateway.

Claude Opus 5.5 is the lower-priced of the two on Router One — about 50% 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 5.2 and Claude Opus 5.5 compared on current per-token rates, context window, and capabilities — both callable through one OpenAI-compatible endpoint that logs each request it forwards.

## Claude Fable 5.2 vs Claude Opus 5.5: rates, context window, and capabilities

| Spec | Claude Fable 5.2 | Claude Opus 5.5 |
| --- | --- | --- |
| Input / 1M tokens | $4.80 | $2.40 |
| Output / 1M tokens | $24.00 | $12.00 |
| Cached input / 1M tokens | $0.12 | $0.40 |
| Context window | 1.05M | 1.05M |
| Capabilities | Chat, Streaming, Tool calling, Vision | Chat, Streaming, Tool calling, Vision |
| Subscription plans | Not in any plan — wallet | Not in any plan — wallet |
| Detail page | [Claude Fable 5.2](https://router.one/models/claude-fable-5-2) | [Claude Opus 5.5](https://router.one/models/claude-opus-5-5) |

## What does 1M tokens cost on Claude Fable 5.2 vs Claude Opus 5.5?

For a workload of 1M input plus 1M output tokens at current rates: Claude Fable 5.2 comes to $28.80, Claude Opus 5.5 comes to $14.40 — Claude Opus 5.5 is about 50% 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 5.2 and Claude Opus 5.5

The API key, base URL and endpoints stay the same: Router One serves both on /v1/messages and /v1/chat/completions, not on /v1/responses, so Claude Code (/v1/messages) runs either model and Codex CLI (/v1/responses) runs neither. Claude Opus 5.5 code may still need changes before it runs on Claude Fable 5.2. Per Anthropic's Claude Fable 5.2 migration guide (checked 2026-11-11), both models always think adaptively on Anthropic's own API, and the changes it lists include these: Claude Fable 5.2's default effort is high where Claude Opus 5.5's is medium, so a request that omits effort runs one level higher; Claude Fable 5.2 enforces the prefix check for every account, so code that edits the system prompt, tools or earlier messages and then sends back a Claude Fable 5.2 thinking block gets a 400 error; and Claude Opus 5.5 cannot read Claude Fable 5.2's thinking blocks, so a conversation moved from Claude Fable 5.2 to Claude Opus 5.5 continues without that reasoning. Anthropic's models overview (checked 2026-11-11) suggests starting with Claude Opus 5.5 for most workloads and using Claude Fable 5.2 for demanding reasoning and long-horizon agentic work, or when evals on Claude Opus 5.5 at higher effort still fall short. On a Pro, Max or Ultra plan the billing does not change: as of the 2026-11-11 plan response, neither Claude Fable 5.2 nor Claude Opus 5.5 is in a plan tier, so both bill the wallet per token.

`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-5.2", "messages": [{"role": "user", "content": "Hello"}]}'

# Same request, other model — change one string:
#   "model": "anthropic/claude-opus-5.5"
```

## FAQ

### Is Claude Fable 5.2 cheaper than Claude Opus 5.5?

Input: Claude Fable 5.2 $4.80 vs Claude Opus 5.5 $2.40 / 1M tokens; Claude Opus 5.5 has the lower rate. Output: Claude Fable 5.2 $24.00 vs Claude Opus 5.5 $12.00 / 1M tokens; Claude Opus 5.5 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.

### Is Claude Fable 5.2 or Claude Opus 5.5 included in a Router One subscription?

Neither Claude Fable 5.2 nor Claude Opus 5.5 is in a Router One plan, so every call to either bills the wallet per token.

### Can I switch between Claude Fable 5.2 and Claude Opus 5.5 without changing code?

The API key, base URL and endpoints stay the same: Router One serves both on /v1/messages and /v1/chat/completions, not on /v1/responses, so Claude Code (/v1/messages) runs either model and Codex CLI (/v1/responses) runs neither. Claude Opus 5.5 code may still need changes before it runs on Claude Fable 5.2. Per Anthropic's Claude Fable 5.2 migration guide (checked 2026-11-11), both models always think adaptively on Anthropic's own API, and the changes it lists include these: Claude Fable 5.2's default effort is high where Claude Opus 5.5's is medium, so a request that omits effort runs one level higher; Claude Fable 5.2 enforces the prefix check for every account, so code that edits the system prompt, tools or earlier messages and then sends back a Claude Fable 5.2 thinking block gets a 400 error; and Claude Opus 5.5 cannot read Claude Fable 5.2's thinking blocks, so a conversation moved from Claude Fable 5.2 to Claude Opus 5.5 continues without that reasoning. Anthropic's models overview (checked 2026-11-11) suggests starting with Claude Opus 5.5 for most workloads and using Claude Fable 5.2 for demanding reasoning and long-horizon agentic work, or when evals on Claude Opus 5.5 at higher effort still fall short. On a Pro, Max or Ultra plan the billing does not change: as of the 2026-11-11 plan response, neither Claude Fable 5.2 nor Claude Opus 5.5 is in a plan tier, so both bill the wallet per token.

### 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 2026-11-11 (UTC) and refresh within the hour.

## More comparisons

- [Claude Opus 5.5 vs GPT-6 Sol](https://router.one/models/compare/claude-opus-5-5-vs-gpt-6-sol)
- [Claude Opus 5.5 vs Claude Sonnet 5](https://router.one/models/compare/claude-opus-5-5-vs-claude-sonnet-5)
- [Claude Sonnet 5.5 vs Claude Opus 5.5](https://router.one/models/compare/claude-sonnet-5-5-vs-claude-opus-5-5)
- [Claude Opus 5.5 vs GPT-6 Astra](https://router.one/models/compare/claude-opus-5-5-vs-gpt-6-astra)

## See also

- Canonical page: https://router.one/models/compare/claude-fable-5-2-vs-claude-opus-5-5
- 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
- Claude Fable 5.2 API guide: https://router.one/blog/claude-fable-5-2-api-guide
- Claude Opus 5.5 API guide: https://router.one/blog/claude-opus-5-5-api-guide
- Claude Code on Opus 5.5: https://router.one/blog/claude-code-opus-5-5-setup
- Migrating to Claude Opus 5.5: https://router.one/blog/claude-opus-5-5-migration-guide
- Cost calculator: https://router.one/llm-cost-calculator
- Pricing methodology: https://router.one/pricing-methodology