Codex CLI 0.137.0 only spawns sub-agents of the same type

What version of Codex CLI is running?

v0.137.0

What subscription do you have?

Pro 20X

Which model were you using?

gpt-5.5

What platform is your computer?

Linux 7.0.10-2-cachyos x86_64

What terminal emulator and version are you using (if applicable)?

Ghostty

Codex doctor report

What issue are you seeing?

Codex 0.137.0 can only spawn subagents of the same type as the default agent. Before, I can tell it to "spawn gpt-5.3-codex-spark-high" while using gpt-5.5-medium. Now, if my default agent is gpt-5.5-medium, the subagents always default to that one.

What steps can reproduce the bug?

1. Install v0.137.0
2. Ask codex to spawn a different subagent type, e.g, the main agent is 5.5, the subagent is 5.4

What is the expected behavior?

The subagent must be spawned according to the user's requested model.

Additional information

_No response_