Claude Fable 5.1 vs GPT-5.5
Claude Fable 5.1 (Anthropic) and GPT-5.5 (OpenAI) 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 | GPT-5.5 |
|---|---|---|
| Developer | Anthropic | OpenAI |
| Released | September 1, 2026 | April 23, 2026 |
| Capability index | 92.6 / 100 | 89 / 100 |
| Input price | $10 | $5 |
| Output price | $50 | $30 |
| Cost of a typical task | $0.30 | $0.16 |
| Context window | 1,000,000 tokens | 1,050,000 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 | December 1, 2025 |
What are we comparing?
Claude Fable 5.1 and GPT-5.5 are two frontier models, the ones you pick when quality comes first, one from Anthropic, the other from OpenAI. Claude Fable 5.1 was released on September 1, 2026, GPT-5.5 on April 23, 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.
Which one is more capable?
On our capability index, Claude Fable 5.1 scores 92.6 out of 100 and GPT-5.5 89. Claude Fable 5.1 leads by 3.6 points.
On the 4 benchmarks reported for both, Claude Fable 5.1 wins 3 times and GPT-5.5 0:
- OTIS Mock AIME (competition mathematics problems): Claude Fable 5.1 100%, GPT-5.5 100%
- FrontierMath (very hard research-level mathematics): Claude Fable 5.1 90.2%, GPT-5.5 85.3%
- FrontierCode (advanced programming tasks): Claude Fable 5.1 50.9%, GPT-5.5 43%
- APEX-Agents (professional tasks carried out by an agent): Claude Fable 5.1 68.6%, GPT-5.5 55.1%
Pricing
Claude Fable 5.1 costs $10 per million input tokens and $50 per million output tokens; GPT-5.5 costs $5 and $30.
For a typical agent task (read 20,000 tokens, write 2,000), expect $0.30 with Claude Fable 5.1 versus $0.16 with GPT-5.5. GPT-5.5 is 1.9 times cheaper, a gap that adds up quickly over 1,000 tasks: $140 difference.
Run the numbers with your own volumes in the agent cost calculator.
Under the hood
GPT-5.5 reads more in one go: 1,050,000 tokens of context (roughly 1,575 pages), versus 1,000,000 for Claude Fable 5.1.
Reasoning mode: Claude Fable 5.1 yes, GPT-5.5 yes. Tool calling: Claude Fable 5.1 yes, GPT-5.5 yes. Image input: Claude Fable 5.1 yes, GPT-5.5 yes.
Neither publishes its weights: both are used through an API.
Knowledge cutoff: June 2026 for Claude Fable 5.1, December 1, 2025 for GPT-5.5.
In short
Our reading of the data:
- Choose Claude Fable 5.1 for a higher capability index and a more recent release.
- Choose GPT-5.5 for 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 GPT-5.5: which is better?
On our index (Epoch AI data), Claude Fable 5.1 scores 92.6 and GPT-5.5 89 out of 100. The best choice also depends on price and on your use case.
Which one is cheaper?
GPT-5.5. To read 20,000 tokens and write 2,000, expect $0.30 with Claude Fable 5.1 and $0.16 with GPT-5.5 (prices as of October 22, 2026).
Which one has the larger context window?
GPT-5.5, with 1,050,000 tokens versus 1,000,000.
Can I run Claude Fable 5.1 or GPT-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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