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

Claude Fable 5.1 had 26% fewer counted bugs per line than Claude Opus 5 (1.17 vs 1.58). Claude Fable 5.1 ranks #4 of 7 and Claude Opus 5 #6.

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

Claude Opus 5, with 38.3% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 19.4% for Claude Fable 5.1.

Updated Sep 26, 2026

Claude Fable 5.1 had 26% fewer counted bugs per line than Claude Opus 5 (1.17 vs 1.58).

Claude Fable 5.1 and Claude Opus 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 Opus 5
Relative bug rate	1.17	1.58
Rank	#4 of 7	#6 of 7
By coding agent
Claude Code	1.17	1.58
Details
Share of AI-written code, week of Sep 14	19.4%	38.3%

1.00 = average · lower is better

Which has fewer bugs, Claude Fable 5.1 or Claude Opus 5?: Claude Fable 5.1 had 26% fewer counted bugs per line than Claude Opus 5 (1.17 vs 1.58). Claude Fable 5.1 ranks #4 of 7 and Claude Opus 5 #6.
Which is used more, Claude Fable 5.1 or Claude Opus 5?: Claude Opus 5, with 38.3% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 19.4% for Claude Fable 5.1.