Users claimed Opus 5.5’s performance has dropped; an independent measurement showed it within the normal range of variation
This story was updated after publication (Oct. 9, 2026). Details
Users on X and Reddit claim that Claude Opus 5.5, which Anthropic released on September 22, has gotten worse since launch. On BridgeMind’s NerfBench, which retests models regularly, Opus 5.5 fell to 94.2% of its launch score on October 2 and stood at 96.5% in the latest test on October 4. BridgeMind treats 90% to 110% as normal variance, so this is not evidence of a downgrade. Only five tests have been run so far, though. Another possible explanation: according to Anthropic’s documentation, Opus 5.5 defaults to medium effort, while Opus 5 defaulted to high.
Sources
- Anthropic, “Introducing Claude Opus 5.5”, (anthropic.com)
- BridgeBench (BridgeMind), “Claude Opus 5.5 — Nerf Bench” (bridgebench.ai)
- BridgeMind (X), post on X: Opus 5.5 drops to 94.2% on NerfBench, (x.com)
- Anthropic (Claude Platform Docs), “Claude Opus 5.5 migration guide” (platform.claude.com)
Corrections and updates
- After this story was published, NerfBench added a sixth measurement on October 9: Opus 5.5 stood at 95.7% of its launch score. That is still within the 90% to 110% range BridgeMind treats as normal variance, so the conclusion is unchanged.
About this story
This story was posted on Instagram by @jarrus.tech on Oct. 5, 2026.
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This story in Turkish: Kullanıcılar Opus 5.5’in performansının düştüğünü iddia etti, bağımsız ölçüm normal dalgalanma aralığında olduğunu gösterdi
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