He isn't talking about ultra mode which you are.

He said "ultrafast" which has nothing to do with subagents. It's a new API tier where it runs on a different inference backend to get you faster token/s.

Huh, yeah, it's not just a portmanteau of "fast" mode + "ultra" reasoning but something completely different, you're right: https://openai.com/index/previewing-ultrafast/

OpenAI really is the worst at naming stuff.