Subagent `resume` runs an incorrect model

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1

Describe the Bug

When calling a Subagent with resume, the Subagent inherits the model from the Agent, not from the resumable Subagent. Reasoning effort is not inherited.

Steps to Reproduce

with not the composer-2-fast model:

Hello.
1. Request a connection test and answer "OK" from the model composer-2-fast
2. Then, resume to the same model asking for "hello world."

Screenshots / Screen Recordings

2026-05-14_08-44-27.png
2026-05-14_08-44-27.png523×428 4.35 KB

Operating System

Windows 10/11

Version Information

Version: 3.4.1 (system setup)
VSCode Version: 1.105.1
Commit: 2a298dd06944a9b9ea541d28225b779fcbcc6200
Date: 2026-05-08T16:05:07.818Z
Layout: editor
Build Type: Stable
Release Track: Nightly
Electron: 39.8.1
Chromium: 142.0.7444.265
Node.js: 22.22.1
V8: 14.2.231.22-electron.0
OS: Windows_NT x64 10.0.22631

For AI issues: add Request ID with privacy disabled

8b99cc0c-030e-4438-845e-f350fbce28fe
ba658273-3c58-4b02-8a2c-9c875c4a9e35

Additional Information

Here are the exact payloads for the four Subagent calls.

1) First run

{
  "description": "Connection test with composer-2-fast",
  "prompt": "Connection test only. Reply with exactly: OK",
  "model": "composer-2-fast",
  "subagent_type": "generalPurpose",
  "readonly": true,
  "run_in_background": false
}

2) Resume of the first run

{
  "description": "Follow-up hello world prompt",
  "prompt": "hello world.",
  "resume": "afbb4674-a581-4066-a60c-afba77445a0c",
  "subagent_type": "generalPurpose",
  "readonly": true,
  "run_in_background": false
}

3) Second run

{
  "description": "New connection test on composer-2-fast",
  "prompt": "Connection test only. Reply with exactly: OK",
  "model": "composer-2-fast",
  "subagent_type": "generalPurpose",
  "readonly": true,
  "run_in_background": false
}

4) Resume of the second run

{
  "description": "Resume with hello world prompt",
  "prompt": "hello world.",
  "resume": "90e0aaba-34a4-403a-be1f-ba746ac5c811",
  "subagent_type": "generalPurpose",
  "readonly": true,
  "run_in_background": false
}

If you want, I can also give you the same payloads as a compact one-line JSON list.

Does this stop you from using Cursor

Yes - Cursor is unusable

4

I would be extremely grateful if I could be notified when the bug has been fixed, as I would now have to add a note to the instructions prohibiting the use of resume.

8

This is a confirmed bug. When a subagent is resumed via resume, the model from the original run is not preserved — it falls back to the parent agent’s model instead. Your usage log confirms gpt-5.4-mini-medium was actually used on the resumed calls instead of composer-2-fast.

This is separate from the display bug we discussed in your earlier thread — here, the wrong model is actually being used, not just displayed incorrectly.

I’ve escalated this to our engineering team. We’ll update this thread when a fix ships. In the meantime, spawning a fresh subagent with an explicit model parameter instead of using resume is the right workaround.

10

Solved in Nightly 3.5.3

11

Broken again in 3.5.11

12

Thanks for reporting back. This is a regression — the fix that shipped in 3.5.3 was inadvertently dropped during a subsequent refactor. I’ve flagged this on the tracking ticket so the team is aware. A re-fix should follow.

13

v3.6.12
Sometimes it works correctly, sometimes it doesn’t.

14

In v3.7.6 with GPT-5.5 as Agent and Composer 2.5 as Subagent works good.