Updated
Claude Fable 5.1 vs Claude Sonnet 5.5
Claude Fable 5.1 (1.12) and Claude Sonnet 5.5 (0.96) are statistically tied on Bug Bench.
| Claude Fable 5.1 | Claude Sonnet 5.5 | |
|---|---|---|
| Bug rate | ||
| Relative bug rate(statistically tied) | 1.12 | 0.96 |
| Rank | #3 of 8 | #2 of 8 |
| By coding agent | ||
| Claude Code(statistically tied) | 1.12 | 0.92 |
| By bug type | ||
| Logic bugs | 1.14 | 0.74 |
| Testing and docs(statistically tied) | 1.37 | 1.29 |
| By language | ||
| TypeScript | 1.35 | 0.54 |
| Python | 0.92 | 1.70 |
| Details | ||
| Provider | Anthropic | Anthropic |
| Released | Sep 1, 2026 | Sep 28, 2026 |
| List price | $10 input / $50 output per 1M tokens | $2 input / $10 output per 1M tokens |
| Share of AI-written code, week of Sep 28 | 6.6% | 2.4% |
1.00 = average · lower is better · = statistically tied
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Questions and answers
- Which has fewer bugs, Claude Fable 5.1 or Claude Sonnet 5.5?
- Claude Fable 5.1 (1.12) and Claude Sonnet 5.5 (0.96) are statistically tied on Bug Bench. Claude Sonnet 5.5 ranks #2 of 8 and Claude Fable 5.1 #3.
- Which is cheaper, Claude Fable 5.1 or Claude Sonnet 5.5?
- Claude Fable 5.1 lists at $10 input / $50 output per 1M tokens; Claude Sonnet 5.5 lists at $2 input / $10 output per 1M tokens. Claude Sonnet 5.5 has the lower list price.
- Does it depend on the programming language?
- In TypeScript, Claude Sonnet 5.5 had the lower rate (0.54 vs 1.35); in Python, Claude Fable 5.1 had the lower rate (0.92 vs 1.70).
- Does it depend on the kind of bug?
- For logic bugs, Claude Sonnet 5.5 had the lower rate (0.74 vs 1.14); for testing and documentation issues, they were statistically tied (1.37 and 1.29).