Claude Opus 5 Debugging Benchmark: Does More Reasoning Actually Fix More Bugs?

More reasoning effort helped on only a small part of AlphaSignal's reported debugging workload. It tested Anthropic's Claude Opus 5 on the same 13 tasks five times at each of four effort settings. The published results report success rising from 93.8% at Low to 98.5% at XHigh, while 11 tasks already succeeded on every Low-effort attempt. The additional successes therefore came from the remaining two tasks. In this small experiment on one private application, the benefit was concentrated in particular bugs rather than spread across every repair.

“A 260-attempt benchmark of Claude Opus 5 across four effort levels found that moving from Low (93.8% resolve rate) to XHigh (98.5%) improved reliability by only 4.7 percentage points while increasing cost per successful fix by 477% and token usage by 635%.”

AlphaSignalAI

“Medium effort emerged as the practical sweet spot, matching High's 63/65 resolve rate at 57% fewer tokens, 38% lower latency, and less than half the cost per fix.”

AlphaSignalAI

“Higher effort levels also changed patch behavior, with XHigh producing an average of 21.9 changed lines versus 11.3 at Low, and generating more over-edit attempts that exceeded expected edit scope.”

AlphaSignalAI

“In cross-model comparison, Opus 5 at XHigh (64/65) was outperformed on reliability, cost, and latency simultaneously by Grok 4.5, GPT-5.6 Sol, and Fable 5, all of which achieved 65/65.”

AlphaSignalAI

“Opus 5 at XHigh produced a more precise set of actionable comments than its production baseline, but caught fewer known issues and generated roughly four times as many nitpicks.”

AlphaSignalAI