effort-calibrator
Effort Calibrator
On Fable 5 and 5.1, effort is the primary dial trading intelligence against latency and cost. Settings inherited from earlier models are usually wrong here, and so are settings inherited from Fable 5 by 5.1: an effort name does not buy the same amount of thinking across generations, so re-run your sweep on 5.1 even if you already tuned Fable 5. Reference points: Fable 5 at lower effort frequently beats earlier models at xhigh; Fable 5.1 at medium roughly matches Fable 5 at lower cost, and at low it often scores higher than Opus and Sonnet models at a similar cost per task, so include it wherever you would otherwise run a smaller model at higher effort.
Starting points by workload
| Workload | Start at |
|---|---|
| Routine transforms, classification, short edits, chat, subagents | medium (try low if latency matters) |
| Most analysis and writing | high (the general default) |
| Coding and agentic/tool-heavy work | high (the API and Claude Code default on Fable 5 and 5.1) — even for workloads that ran at xhigh on earlier Opus models; escalate to xhigh only for the most capability-sensitive tasks |
| Hardest capability-sensitive work: large migrations, multi-day autonomous runs, novel research | xhigh — on 5.1 this is where the gains over Fable 5 are largest, at the price of longer thinking before the first response |
Frontier problems only, where evals show headroom above xhigh and token spend is unconstrained |
max |
The signal for max is evals showing headroom above xhigh on your actual task: on most workloads it adds significant cost for small gains and can tip into overthinking.