Endless thinking loop in Plan Mode subagent

[Marek_Nevole]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Running Plan mode, with the following prompt

I want to support scikit-learn API in my package. Create new submodule in the package . Also write the compatiblity tests.

spins up a subagent(?) that is stuck in a loop and burns through my tokens.

Steps to Reproduce

Input the prompt to fresh planning mode chat

Expected Behavior

The regular planning mode’s expected behavior.

Screenshots / Screen Recordings

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.4.7
VSCode Version: 1.105.1
Commit: ca0f9bf806f235ea014a22712cbcbf5e88ca77e0
Date: 2026-01-20T20:52:38.077Z
Build Type: Stable
Release Track: Early Access
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 24.6.0

For AI issues: which model did you use?

Tried Opus 4.5, GPT 5.2 Codex, Gemini 3 Flash

Does this stop you from using Cursor

Yes - Cursor is unusable

[deanrie]

Hey, thanks for the report.

I can see the issue: the subagent “Explore gemss codebase for scikit-learn API integration” got stuck in a loop, endlessly repeating:

</think>
Reviewing key files to understand the current API.

This looks like a bug with parsing the thinking tags. The model can’t properly exit the “think” block and ends up looping.

If you can, please send the Request ID (chat menu > Copy Request ID). It’ll help with debugging.

[Curtis_Renkiewicz]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Agent is just doing this weird thinking thing over and over. However if I switch to Opus it is all working fine.

Steps to Reproduce

Just try to use agent mode in any chat with composer 1 as the model

Expected Behavior

Work as normal doing planning, tool calls, etc..

Screenshots / Screen Recordings

Operating System

MacOS

Version Information

Version: 2.4.21
VSCode Version: 1.105.1
Commit: dc8361355d709f306d5159635a677a571b277bc0
Date: 2026-01-22T16:57:59.675Z
Build Type: Stable
Release Track: Early Access
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 24.6.0

For AI issues: which model did you use?

composer 1

For AI issues: add Request ID with privacy disabled

97743c41-a80c-4fd3-888a-f39e5098df00

Does this stop you from using Cursor

No - Cursor works, but with this issue

[condor (Condor (Tee))]

hi @Curtis_Renkiewicz and welcome to Cursor Forum. Thank you for your detailed bug report.

We are already aware of this issue and a fix is on the way.

[Jair_Lomas]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

When I use ASK agent mode, I ask for something and cursor get stuck in loop.

Steps to Reproduce

Select code.
Switch to ask agent mode.
Describe instructions.
Enter.

Screenshots / Screen Recordings

Operating System

MacOS

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.3.41 (Universal)
VSCode Version: 1.105.1
Commit: 2ca326e0d1ce10956aea33d54c0e2d8c13c58a30
Date: 2026-01-16T19:14:00.150Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 24.6.0

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor

[Freshman (Heartruler)]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

When I use ASK agent mode, I ask for something and cursor get stuck in loop. Btw, plan mode also has this problem.

Steps to Reproduce

Select code.
Switch to ask agent mode.
Describe instructions.
Enter.

**Screenshots / Screen Recordings

(ASK Mode) Although it is Chinese, you can obviously find that it is a loop cause Cursor keep answering the same words.

Operating System**
windows10

Current Cursor Version (Menu → About Cursor → Copy)

Version: 2.4.21 (system setup)
VSCode Version: 1.105.1
Commit: dc8361355d709f306d5159635a677a571b277bc0
Date: 2026-01-22T16:57:59.675Z
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: Windows_NT x64 10.0.19045

For AI issues: which model did you use?

composer 1

For AI issues: add Request ID with privacy disabled

16b9dfd5-3b03-4387-ac46-4fd7d0e657c6

Does this stop you from using Cursor

Yes, this stupid thinking loop stocks Cursor.