Detailed comparison of capabilities, features, and performance.
| Feature | GPT-5.5 | Claude Fable 5 |
|---|---|---|
| AI Lab | OpenAI | Anthropic |
| Context Size | 1,050,000 tokens | 1,000,000 tokens |
| Max Output Size | 128,000 tokens | 128,000 tokens |
| Frontier Model | Yes | Yes |
| Vision Support | Yes | Yes |
| Description | OpenAI's newest frontier model for the most complex professional work. Features 1.05M context window, 128k output tokens, and reasoning token support. Reasoning.effort supports: none, low, medium (default), high and xhigh. | Anthropic's most capable widely released model, with a 1M token context window, 128k max output, and always-on adaptive thinking. |
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