Shane Melaugh flags Claude Opus 5.5 reasoning shift after November 3

Shane Melaugh's analysis covered Claude Code sessions from October 9 to November 7, 2026, and pointed to a change around November 3. The share of sentences beginning with "I'm" rose to 61.3%, while "I should" and "I need to" fell to 10.9%, and dash usage dropped to 6.5%. He also noted that the change occurred around 3:00 a.m. Japan time on November 4 and appeared in seven sessions that were active at the time.

Anthropic's official materials state that the thinking shown to users in Claude Code is not the model's raw internal processing but a summary produced by another AI model. That means a change to the summarization mechanism alone could alter the visible text. Developer Theo Brown, who examined about 458,000 Claude Opus 5.5 responses, suggested Anthropic may be rolling out a change to the reasoning summarizer on a per-account basis, with timing varying from October 30 to November 4. He said he found no sign of degraded capability in his environment.

Melaugh described his investigation as not a scientifically rigorous performance evaluation, and said it began from his personal experience. Reports of perceived performance drops have also appeared on Hacker News, alongside opinions that only the summarization method changed. As of writing, it remains unclear whether Claude Opus 5.5's reasoning ability actually declined, and further explanation from Anthropic and additional verification are awaited.