Claude Fable 5.1 or Claude Opus 5.5: which to choose?
Claude Fable 5.1 (Anthropic) and Claude Opus 5.5 (Anthropic) compared point by point: measured performance, pricing, context and capabilities.
Data as of October 22, 2026
Side-by-side comparison
| Criterion | Claude Fable 5.1 | Claude Opus 5.5 |
|---|---|---|
| Developer | Anthropic | Anthropic |
| Released | September 1, 2026 | September 22, 2026 |
| Capability index | 92.6 / 100 | 95.9 / 100 |
| Input price | $10 | $4 |
| Output price | $50 | $20 |
| Cost of a typical task | $0.30 | $0.12 |
| Context window | 1,000,000 tokens | 1,000,000 tokens |
| Maximum output | 128,000 tokens | 128,000 tokens |
| Reasoning mode | Yes | Yes |
| Tool calling | Yes | Yes |
| Accepted inputs | text, image, PDF | text, image, PDF |
| Open weights | No | No |
| Knowledge cutoff | June 2026 | June 2026 |
Two models head to head
This comparison pits two frontier models, the ones you pick when quality comes first against each other: Claude Fable 5.1 and Claude Opus 5.5, both built by Anthropic. The first dates from September 1, 2026, the second from September 22, 2026.
All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.
Performance
On our capability index, Claude Fable 5.1 scores 92.6 out of 100 and Claude Opus 5.5 95.9. Claude Opus 5.5 leads by 3.3 points.
On the 4 benchmarks reported for both, Claude Fable 5.1 wins 0 times and Claude Opus 5.5 3:
- OTIS Mock AIME (competition mathematics problems): Claude Fable 5.1 100%, Claude Opus 5.5 100%
- FrontierMath (very hard research-level mathematics): Claude Fable 5.1 90.2%, Claude Opus 5.5 91.2%
- FrontierCode (advanced programming tasks): Claude Fable 5.1 50.9%, Claude Opus 5.5 54.6%
- APEX-Agents (professional tasks carried out by an agent): Claude Fable 5.1 68.6%, Claude Opus 5.5 73.5%
Pricing
Claude Fable 5.1 costs $10 per million input tokens and $50 per million output tokens; Claude Opus 5.5 costs $4 and $20.
For a typical agent task (read 20,000 tokens, write 2,000), expect $0.30 with Claude Fable 5.1 versus $0.12 with Claude Opus 5.5. Claude Opus 5.5 is 2.5 times cheaper, a gap that adds up quickly over 1,000 tasks: $180 difference.
Run the numbers with your own volumes in the agent cost calculator.
Features and limits
Both models have the same context window: 1,000,000 tokens, roughly 1,500 pages.
Reasoning mode: Claude Fable 5.1 yes, Claude Opus 5.5 yes. Tool calling: Claude Fable 5.1 yes, Claude Opus 5.5 yes. Image input: Claude Fable 5.1 yes, Claude Opus 5.5 yes.
Neither publishes its weights: both are used through an API.
Knowledge cutoff: June 2026 for Claude Fable 5.1, June 2026 for Claude Opus 5.5.
In short
Our reading of the data:
- Choose Claude Opus 5.5 for a higher capability index and a lower cost.
This verdict relies on public figures; it does not replace a trial on your own tasks.
Other comparisons
Frequently asked questions
Claude Fable 5.1 or Claude Opus 5.5: which is better?
On our index (Epoch AI data), Claude Fable 5.1 scores 92.6 and Claude Opus 5.5 95.9 out of 100. The best choice also depends on price and on your use case.
Which one is cheaper?
Claude Opus 5.5. To read 20,000 tokens and write 2,000, expect $0.30 with Claude Fable 5.1 and $0.12 with Claude Opus 5.5 (prices as of October 22, 2026).
Which one has the larger context window?
Neither: both accept 1,000,000 tokens.
Can I run Claude Fable 5.1 or Claude Opus 5.5 on my own servers?
No: both are closed models, available through an API.
Data sources
- Models.dev — Model data: models.dev (open-source project)
- OpenRouter — Market prices cross-checked with OpenRouter
- Epoch AI — AI Benchmarking Hub — Epoch AI, “AI Benchmarking Hub”, epoch.ai, CC BY 4.0
Data as of October 22, 2026
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