For pro mode the agents worked independently and only when they all finished did a new agent take a look at everything to merge the work into a single response. The new thing involves subagents that have been trained to cooperatively pursue a task and are allowed to communicate with each other along the way.

I imagine this is something like Anthropic's dynamic workflows where a JS file is created to make a little AI harness on the spot

How is this any different than what we have already? We've had this ability for ages (6+ months, decades in the AI world), you can literally today easily prompt CC or Codex to use subagents to accomplish tasks and they'll do it well. My entire workflow is one top level orchestrator chat creating tickets to dispatch to subagents to implement, and other subagents to verify. Why is this being sold as a new thing? Have HN users never tried tried asking CC or Codex to use subagents?

Pro also makes you ask it to use sub-agents instead of just doing it when useful.

Hopefully, 5.6 will automatically spawn sub-agents without needing to ask.

i would believe this will be matched with something like orchestrator-focused model: https://news.ycombinator.com/item?id=48624782