Why does Cursor always fail to edit the plan the first time?

[Charlie_Hess]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I’m using Opus 4.6 but it’s been reproducible with every Anthropic model, and maybe more. When using plan mode, the first time I give it feedback that requires editing the plan, it writes a bunch in its CoT and then, without fail, I get hit with “Edit attempted” “String to replace was not found.” It’s so consistent with Plan mode that this tells me it’s likely something about Cursor or the Plan file format. It’s infuriating and time / token-wasting.

Steps to Reproduce

If you’ve been using Cursor + Opus + Plan mode yourself, I’m 100% sure you’ve already seen it! It’s literally a topic in the groupchat.

Operating System

MacOS

Version Information

Version: 2.4.31 (Universal)
VSCode Version: 1.105.1
Commit: 3578107fdf149b00059ddad37048220e41681000
Date: 2026-02-08T07:42:24.999Z
Build Type: Stable
Release Track: Default
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 25.2.0

For AI issues: which model did you use?

Opus 4.6

Does this stop you from using Cursor

No - Cursor works, but with this issue

[deanrie]

Hey, thanks for the report. A similar plan update bug was tracked before and marked as fixed, but based on your description, it looks like the issue came back in a different form in 2.4.31.

So I can pass this to the engineers with the right context, can you share the Request ID from one of the failed attempts? (Chat menu in the top right, then Copy Request ID). Ideally from the moment it first fails with “String to replace was not found”.

I’ll pass this to the team.