Which has fewer bugs, Claude Fable 5.1 or Claude Sonnet 5?

Claude Fable 5.1 had 44% fewer counted bugs per line than Claude Sonnet 5 (1.17 vs 2.10). Claude Fable 5.1 ranks #4 of 7 and Claude Sonnet 5 #7.

Which is used more, Claude Fable 5.1 or Claude Sonnet 5?

Claude Fable 5.1, with 19.4% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 4.0% for Claude Sonnet 5.

Updated Sep 26, 2026

Claude Fable 5.1 had 44% fewer counted bugs per line than Claude Sonnet 5 (1.17 vs 2.10).

Claude Fable 5.1 and Claude Sonnet 5 compared on relative bug rate, by coding agent, bug type, and language, and on price and usage.
Bug rate
	Claude Fable 5.1	Claude Sonnet 5
Relative bug rate	1.17	2.10
Rank	#4 of 7	#7 of 7
By coding agent
Claude Code	1.17	2.12
Details
Share of AI-written code, week of Sep 14	19.4%	4.0%

1.00 = average · lower is better

Which has fewer bugs, Claude Fable 5.1 or Claude Sonnet 5?: Claude Fable 5.1 had 44% fewer counted bugs per line than Claude Sonnet 5 (1.17 vs 2.10). Claude Fable 5.1 ranks #4 of 7 and Claude Sonnet 5 #7.
Which is used more, Claude Fable 5.1 or Claude Sonnet 5?: Claude Fable 5.1, with 19.4% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 4.0% for Claude Sonnet 5.