Which has fewer bugs, Claude Fable 5.1 or GPT-5.6 Luna?

Claude Fable 5.1 (1.17) and GPT-5.6 Luna (1.28) are statistically tied on Bug Bench. Claude Fable 5.1 ranks #4 of 7 and GPT-5.6 Luna #5.

Which is used more, Claude Fable 5.1 or GPT-5.6 Luna?

Claude Fable 5.1, with 19.4% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 1.7% for GPT-5.6 Luna.

Updated Sep 26, 2026

Claude Fable 5.1 (1.17) and GPT-5.6 Luna (1.28) are statistically tied on Bug Bench.

Claude Fable 5.1 and GPT-5.6 Luna compared on relative bug rate, by coding agent, bug type, and language, and on price and usage.
Bug rate
	Claude Fable 5.1	GPT-5.6 Luna
Relative bug rate(statistically tied)	1.17	1.28
Rank	#4 of 7	#5 of 7
Details
Share of AI-written code, week of Sep 14	19.4%	1.7%

1.00 = average · lower is better · = statistically tied

Which has fewer bugs, Claude Fable 5.1 or GPT-5.6 Luna?: Claude Fable 5.1 (1.17) and GPT-5.6 Luna (1.28) are statistically tied on Bug Bench. Claude Fable 5.1 ranks #4 of 7 and GPT-5.6 Luna #5.
Which is used more, Claude Fable 5.1 or GPT-5.6 Luna?: Claude Fable 5.1, with 19.4% of the AI-written code reviewed by cubic in the week of Sep 14, 2026, against 1.7% for GPT-5.6 Luna.