Updated
Which AI model writes the most logic bugs?
As of Sep 27, 2026, Claude Sonnet 5 had the highest rate of logic bugs, 87% above the all-model rate (1.87). GPT-5.5 had the lowest, 48% below average (0.52).
| Rank | Model | Rate |
|---|---|---|
| 1 | GPT-5.5 | 0.52 |
| 2= (statistically tied) | Claude Fable 5 | 0.70 |
| 3= (statistically tied) | GPT-5.6 Sol | 0.71 |
| 4 | Claude Opus 4.8 | 0.95 |
| 5= (statistically tied) | GPT-6 Astra | 1.07 |
| 6= (statistically tied) | Claude Fable 5.1 | 1.19 |
| 7= (statistically tied) | GPT-5.6 Luna | 1.32 |
| 8 | Claude Opus 5 | 1.52 |
| 9 | Claude Sonnet 5 | 1.87 |
1.00 = all-model rate · lower is better · = statistically tied