# @QiaochuYuan — 2026-07-28

♥479 ↻20 · https://x.com/QiaochuYuan/status/2081958293195612612

this is incredibly weird, seems to put opus 5 in some kind of base model-like mode for no obvious reason? here's 4 consecutive runs in incognito, also when asked afterwards opus reverts to normal and can't seem to really tell it's done something weird https://t.co/UcAYaG10PI

![photo](../../../media/HOSY3kPasAAOqSg.jpg)
![photo](../../../media/HOSZr__bYAA64Lm.jpg)
![photo](../../../media/HOSZ1SNagAEiU27.jpg)
![photo](../../../media/HOSZ-Y5boAAWqk6.jpg)
tags: author:qiaochuyuan, base-models, has-image, kind:image, kind:tweet, on:claude-opus-5, year:2026
cited on: claude-opus-5