Which AI model writes the most bugs in Codex?

As of Nov 9, 2026, GPT-6 Astra had the highest relative bug rate in Codex (0.96, 4% fewer counted bugs than the all-model average).

How much AI-written code comes from Codex?

Codex wrote 16.1% of the AI-written code reviewed by cubic in the week of Nov 2, 2026.

Updated Nov 9, 2026

Best AI model for Codex

As of Nov 9, 2026, GPT-6 Luna had the lowest relative bug rate in Codex (0.31, 69% fewer counted bugs than the all-model average), among 3 ranked models.

Models ranked by relative bug rate for code written in Codex. Lower values are better.
Rank	Model	Rate
1	GPT-6 Luna	0.31
2	GPT-6.1 Sol	0.72
3	GPT-6 Astra	0.96

1.00 = all-model average · lower is better

How widely Codex is used

Share of AI-written code reviewed by cubic

Latest weekWeek of Nov 2: 16.1%
Peak weekWeek of Aug 24: 38.9%

Other coding agents

Claude Code
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Questions and answers

Which AI model writes the most bugs in Codex?: As of Nov 9, 2026, GPT-6 Astra had the highest relative bug rate in Codex (0.96, 4% fewer counted bugs than the all-model average).
How much AI-written code comes from Codex?: Codex wrote 16.1% of the AI-written code reviewed by cubic in the week of Nov 2, 2026.