codex - 💡(How to fix) Fix Creating sub-agent hangs on MCP startup [1 participants]

TL;DR

The issue might be related to the recent update of Codex CLI to version 0.125.0, causing sub-agents to get stuck during startup on MCP.

Guidance

• Verify if the issue persists when using the same sub-agent configuration with a different model or level of reasoning to isolate the problem.
• Check if the specified sub-agent configuration toml file is correctly formatted and if the model version (gpt-5.4 high) is compatible with the main agent's model (gpt-5.5 xhigh).
• Try creating sub-agents without specifying a custom configuration toml file to see if the issue is related to the custom configuration.
• Compare the behavior between the Codex app and CLI to identify any potential differences in how sub-agents are created or configured.

Notes

The issue might be specific to the combination of the main agent's model, sub-agent's model, and the custom configuration file. Further investigation is needed to determine the root cause.

Recommendation

Apply workaround: Try creating sub-agents without the custom configuration toml file or with a different model version to see if the issue persists. This can help identify if the problem is related to the custom configuration or the model compatibility.