Which AI model writes the most bugs in Swift?

As of Sep 30, 2026, Claude Opus 4.8 had the highest relative bug rate in Swift code (1.42, 42% more counted bugs than the Swift average), statistically tied with GPT-6 Astra and GPT-5.6 Sol.

Updated Sep 30, 2026

Best AI model for Swift code

As of Sep 30, 2026, Claude Opus 5.5 had the lowest relative bug rate in Swift code (0.40, 60% fewer counted bugs than the Swift average), statistically tied with Claude Opus 5 and GPT-6 Astra, among 5 ranked models.

Models ranked by relative bug rate in Swift code. Lower values are better.
Rank	Model	Rate
1= (statistically tied)	Claude Opus 5.5	0.40
2= (statistically tied)	Claude Opus 5	0.80
3= (statistically tied)	GPT-6 Astra	0.91
4= (statistically tied)	GPT-5.6 Sol	1.01
5= (statistically tied)	Claude Opus 4.8	1.42

1.00 = Swift average · lower is better · = statistically tied

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Questions and answers

Which AI model writes the most bugs in Swift?: As of Sep 30, 2026, Claude Opus 4.8 had the highest relative bug rate in Swift code (1.42, 42% more counted bugs than the Swift average), statistically tied with GPT-6 Astra and GPT-5.6 Sol.