Detailed comparison of capabilities, features, and performance.
| Feature | GPT-5.1 codex | Claude Fable 5 |
|---|---|---|
| AI Lab | OpenAI | Anthropic |
| Context Size | 400,000 tokens | 1,000,000 tokens |
| Max Output Size | 128,000 tokens | 128,000 tokens |
| Frontier Model | Yes | Yes |
| Vision Support | Yes | Yes |
| Description | A version of GPT-5.1 optimized for agentic coding tasks. | Anthropic's most capable widely released model, with a 1M token context window, 128k max output, and always-on adaptive thinking. |
View detailed specifications and capabilities
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