Comment by theptip

Yeah I think having a detailed mental model of what it’s actually doing helps.

At least for Fable/Opus (didn’t confirm for Sol yet) Ultra means “write an ephemeral programmatic harness encoding this workflow”. There is actually a TS harness that gets run for the workflow.

If you have a task where the agent/sub-agent pattern works, Ultra just adds indirection.

I think it is possible to get an intuition for an individual model but really you need to eval to be sure. My heuristic though is if you need to treat each work item differently depending on the results, probably agent/subagent. If you want to do the same steps across some queue / tree / DAG of work items, ultra is a better bet. (Or actually write a durable scaffold if you are going to repeatedly run it over > thousands of items.)