Multi-agent unexpectedly created ~12 sessions despite a ~4-agent limit, consuming ~50% of 5-hour quota in ~10 seconds

What version of the Codex App are you using (From “About Codex” dialog)?

26.820.71523

What subscription do you have?

GPT Plus

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

I encountered an unexpected multi-agent fan-out issue in Codex App while using Target mode, with Terra XHigh as the main model.

My original prompt explicitly limited the number of subagents. The relevant part was:

[private research workflow redacted] Please use at most 2 Sol XHigh subagents to complete these tasks. If the specified task is encountered, assign 2 Terra XHigh subagents to it.

Therefore, even under the broadest interpretation of my prompt, I expected:

• 1 Terra XHigh main agent
• at most 2 Sol XHigh subagents
• at most 2 Terra XHigh subagents for the specified task, if applicable

In other words, I expected at most approximately 4 subagents, plus the main Terra XHigh agent.

I did not instruct any subagent to recursively spawn additional agents or create additional independent sessions.

However, Codex unexpectedly created approximately 12 separate sessions (K01-K12) within a very short period of time, together with additional subagent activity.

At approximately the same time, around 50% of my 5-hour usage quota was consumed within roughly 10 seconds.

What steps can reproduce the bug?

Relevant configuration

• Mode: Target
• Main model: Terra XHigh
• Requested Sol subagents: at most 2 Sol XHigh
• Requested Terra subagents: 2 Terra XHigh for the specified task, if applicable
• Expected maximum subagents: approximately 4
• Expected maximum active agents including the main agent: approximately 5
• Observed newly created sessions: approximately 12
• Observed quota impact: ~50% of the 5-hour limit in ~10 seconds

What is the expected behavior?

I expected the Terra XHigh main agent to orchestrate no more than approximately 4 explicitly requested subagents.

Additional information

_No response_