In my tests, as of this morning on the latest Codex SDK, this is not happening for sub-agent requests made in my own harness to other model providers treated as sub-agents.
Specifically, I use Opus and others for subagent execution to get alloyed properties on the workflow, and as far as I can tell, that's not affected.
Presumably, this is to hide optimizations they might be making to their own subagent processing, but that's a losing, dumb battle to fight, and misses the forest for the trees.
> this is not happening for sub-agent requests made in my own harness to other model providers treated as sub-agents.
Obviously it doesn't, how even could it? Read the issue description, it wouldn't make sense if something like that was possible, considering how it was implemented...