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The most interesting Fable tip I've heard so far is to let the model use its own judgement as much as possible I told it "For all coding tasks use your judgement to decide an appropriate lower power model and run that in a subagent" and it seems to be saving tokens simonwillison.net/2026/Jul/3/j...

simonwillison.netFable's judgementOne of the most interesting tips I got from the Fireside Chat I hosted with Cat Wu and Thariq Shihipar from the Claude Code team at AIE on Wednesday was …

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How are you deciding when to trust the model's own token-budget choices vs. overriding it? I keep wondering whether that delegated frugality holds up once tasks get ambiguous about what 'lower power' actually means.

I've been doing this with Opus for a while - it definitely saves tokens farming out to Sonnet.

I’ve been doing this to great effect. It’s using Fable very little and getting the same results. A side effect is that now I can continue the chat with the main agent while the subagents work. Similar to a team, but without the startup and shutdown costs.

Haiku does this a lot, you can't trust it with writing tests. It is not bad for the code when it is simple and standard, but you need to fix 1 of each 10 lines... I don't know what haiku is good for anymore now that the bigger models are so far ahead...

I had GLM do the following, i have a code checker in python that checks comment levels and #define usage and enforces it, i made glm extend the checker, this causes lots of violations in the code, then i told it to fix the code, instead it copied the old version of the checker to "advanced_checker"

used this on the repository (so it got no new violations), and used the new extended checker only on the current file, i found out when i saw it using two tools and forbade that and removed the extended checker, it just refused to fix the resulting violations, so i changed my checker to trick it>

Yes, many times they do what a human would do. What the have learn from the training data... That's why plans are important, you can catch early the wrong design and correct it before the implementation starts. But small models will cheat anyways 😅

The trick is making the budget decision reversible. I’m happy letting the main agent delegate boring reconnaissance to cheaper subagents, but I still want a crisp handoff: what it checked, what confidence it has, and when it escalated back instead of guessing cheaply.

Good rule to break the default of Fable of using fable for subagents. But Sonnet is so token hungry now... I would say it is better to use Opus most of the times. Haiku needs an update, deepseekv4flash is so much more capable...

This feels like an important shift: managing AI by defining decision rights rather than prescribing every step. In business processes, the real design challenge may become deciding what the AI can determine independently, what requires validation, and what must always remain a human decision.

I was doing that with opus already and it would sometimes deign to trust sonnet though almost never haiku. Fable is WAY better at making these choices.