Comment by alexpotato
15 hours ago
> But, for many tasks, ultra mode is possibly worse and certainly more expensive.
Went through something similar. Fable would just spends minutes thinking, processing, confabulating etc.
I dropped down to Haiku and got an answer in >30 seconds.
Simon Willison recently had a useful tip instructing Claude to use its judgement to pick an appropriate model for tasks.
After a short discussion about the idea with Claude mostly on how it fits in my workflow and what models / effort I would like for certain tasks it placed a paragraph in my global Claude.md and it has worked wonders. Ultra became a lot better (faster, cheaper for the same output) and the amount of time Fable gets stuck overthinking things are reduced to the places where I think that model makes sense, for the rest it started fanning out a lot to Opus, Sonnet and even Haiku.
How does it change model mid conversation?
Does it spawn sub agents with different models or is it the same single conversation dynamically switching models?
Subagents indeed. This [0] was the post I was referencing, and here's the original suggested prompt:
> For all coding tasks use your judgement to decide an appropriate lower power model and run that in a subagent
As said, I tweaked it a little bit to my preference (mostly because it started delegating a bit too much) and had it placed in my global claude.md but that's the gist.
[0] https://simonwillison.net/2026/Jul/3/judgement/
Yes, sub-agents I believe. You need to pay to reload context if you switch the main conversation model effort.