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Claude Opus 5.5 and Claude Code

2 products from Anthropic

Quality report · Measured

Livenerf starts a 30-day test of whether Opus 5.5 gets worse after launch

Livenerf runs a frozen 78-question panel (from GPQA Diamond, MMLU-Pro, competition math and AIME) through headless Claude Code on a Max plan, 90 samples a day for 30 days starting September 24, 2026, with a pinned CLI and exact-match grading. The Hacker News launch thread drew 926 points and 394 comments.

Who is affected:
Claude Max subscribers who suspect Opus 5.5 has been quietly downgraded.
What to do:
No action needed. Watch for the first decision around October 24, 2026.

Source

"livenerf is a small, boring, append-only benchmark for one question: does a model get worse after it ships?"

Livenerf GitHub README

Published

Open the sourcegithub.com

Another source

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