Users question Opus 5.5 performance changes
The gist
Developer Shane Melaugh's analysis of 1,400 Claude Code sessions found Opus 5.5's reasoning shifted sharply after Nov 3.
Anthropic hasn't confirmed a change, so users can't tell what shifted.
How it unfolded
- Sep 22, 2026Anthropic released Claude Opus 5.5, the first model in the 5.5 family, at $4 per million input tokens and $20 per million output tokens, down from $5 and $25.
- Oct 26, 2026A GitHub report was filed in which a user measured how often they had to correct Opus 5.5's answers.
- Nov 3, 2026Shane Melaugh's analysis of 1,400 Claude Code sessions found the way Opus 5.5 reasons took a sharp turn, though the model name did not change. Tech Meets East published a video titled "Anthropic Says Opus 5.5 isn't discontinued, I say they are liars".
Key terms
- Claude Code
- A series of large language models developed by Anthropic, released as an AI chatbot and used in software development.
- post-mortem
- A process of identifying the causes of a project failure and how to prevent them in the future.
Source: Wikipedia