Which AI model writes the most bugs in Claude Code?

As of Nov 9, 2026, Claude Opus 5.5 had the highest relative bug rate in Claude Code (1.09, 9% more counted bugs than the all-model average), statistically tied with Claude Sonnet 5.5.

How much AI-written code comes from Claude Code?

Claude Code wrote 79.4% of the AI-written code reviewed by cubic in the week of Nov 2, 2026.

Updated Nov 9, 2026

Best AI model for Claude Code

As of Nov 9, 2026, Claude Fable 5.1 had the lowest relative bug rate in Claude Code (0.88, 12% fewer counted bugs than the all-model average), among 3 ranked models.

Models ranked by relative bug rate for code written in Claude Code. Lower values are better.
Rank	Model	Rate
1	Claude Fable 5.1	0.88
2= (statistically tied)	Claude Sonnet 5.5	1.03
3= (statistically tied)	Claude Opus 5.5	1.09

1.00 = all-model average · lower is better · = statistically tied

How widely Claude Code is used

Share of AI-written code reviewed by cubic

Latest weekWeek of Nov 2: 79.4%
Peak weekWeek of Oct 26: 79.8%

Other coding agents

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Questions and answers

Which AI model writes the most bugs in Claude Code?: As of Nov 9, 2026, Claude Opus 5.5 had the highest relative bug rate in Claude Code (1.09, 9% more counted bugs than the all-model average), statistically tied with Claude Sonnet 5.5.
How much AI-written code comes from Claude Code?: Claude Code wrote 79.4% of the AI-written code reviewed by cubic in the week of Nov 2, 2026.