Opus 4.5 erased 3/6 files which it writes in

[Artemonim]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Opus 4.5 Thinking, in a chat that continued after another model, deleted 3 of the 6 files that it was trying to make changes to.

Steps to Reproduce

…

Screenshots / Screen Recordings

Operating System

Windows 10/11

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.1.39 (user setup)
VSCode Version: 1.105.1
Commit: 60d42bed27e5775c43ec0428d8c653c49e58e260
Date: 2025-11-27T02:30:49.286Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Windows_NT x64 10.0.22631

For AI issues: which model did you use?

Opus 4.5 Thinking

For AI issues: add Request ID with privacy disabled

ba909617-9136-4c26-9999-3ddea1ef3197

Does this stop you from using Cursor

Yes - Cursor is unusable

[deanrie]

Hey, thanks for the report.

Switching models mid-chat can lead to unexpected results, as the new model may misinterpret the conversation context or file state from the previous model.

To help us investigate: Could you share which model you were using before switching to Opus 4.5 Thinking?

[Artemonim]

Gemini 3 Pro Preview. And this is the chat that was reverted to checkpoint.

[Artemonim]

[Artemonim]

By the way, this also repeats the behavior in which returning to the checkpoint does not return erased files. You need to either Undo in the editor or undo the changes via git.,

[Artemonim]

@deanrie

Could you share which model you were using before

Looks like Gemini 3 is corrupting the chats it’s involved in.