Updated
Claude Fable 5.1 vs Claude Opus 5.5
Claude Fable 5.1 had 21% fewer counted bugs per line than Claude Opus 5.5 (0.88 vs 1.11).
| Claude Fable 5.1 | Claude Opus 5.5 | |
|---|---|---|
| Bug rate | ||
| Relative bug rate | 0.88 | 1.11 |
| Rank | #3 of 7 | #6 of 7 |
| By coding agent | ||
| Claude Code | 0.88 | 1.09 |
| By language | ||
| TypeScript(statistically tied) | 1.05 | 1.02 |
| JavaScript(statistically tied) | 1.09 | 1.28 |
| Python | 0.83 | 1.01 |
| Go(statistically tied) | 1.27 | 1.22 |
| Rust(statistically tied) | 1.34 | 1.19 |
| Ruby | 0.41 | 0.98 |
| PHP | 2.53 | 0.82 |
| SQL(statistically tied) | 1.12 | 0.73 |
| Shell(statistically tied) | 0.69 | 1.01 |
| Vue | 0.40 | 1.39 |
| Terraform(statistically tied) | 0.82 | 0.94 |
| Details | ||
| Provider | Anthropic | Anthropic |
| Released | Sep 1, 2026 | Sep 22, 2026 |
| List price | $10 input / $50 output per 1M tokens | $4 input / $20 output per 1M tokens |
| Share of AI-written code, week of Nov 2 | 2.8% | 66.2% |
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 Opus 5.5?
- Claude Fable 5.1 had 21% fewer counted bugs per line than Claude Opus 5.5 (0.88 vs 1.11). Claude Fable 5.1 ranks #3 of 7 and Claude Opus 5.5 #6.
- Which is cheaper, Claude Fable 5.1 or Claude Opus 5.5?
- Claude Fable 5.1 lists at $10 input / $50 output per 1M tokens; Claude Opus 5.5 lists at $4 input / $20 output per 1M tokens. Claude Opus 5.5 has the lower list price.
- Does it depend on the programming language?
- In TypeScript, they were statistically tied (1.05 and 1.02); in JavaScript, they were statistically tied (1.09 and 1.28); in Python, Claude Fable 5.1 had the lower rate (0.83 vs 1.01); in Go, they were statistically tied (1.27 and 1.22); in Rust, they were statistically tied (1.34 and 1.19); in Ruby, Claude Fable 5.1 had the lower rate (0.41 vs 0.98); in PHP, Claude Opus 5.5 had the lower rate (0.82 vs 2.53); in SQL, they were statistically tied (1.12 and 0.73); in shell scripts, they were statistically tied (0.69 and 1.01); in Vue, Claude Fable 5.1 had the lower rate (0.40 vs 1.39); in Terraform, they were statistically tied (0.82 and 0.94).
- Which is used more, Claude Fable 5.1 or Claude Opus 5.5?
- Claude Opus 5.5, with 66.2% of the AI-written code reviewed by cubic in the week of Nov 2, 2026, against 2.8% for Claude Fable 5.1.