| name | effort-calibrator |
| description | Choose and tune the effort setting for Claude Fable 5 workloads. Use whenever the user asks which effort level to use ("what effort should this batch job run at?", "is xhigh worth it here?"), complains that Fable 5 is slow or expensive, wants to cut latency or token cost, designs a pipeline/harness that mixes routine and hard tasks, or reviews API code that sets output_config.effort. |
Effort Calibrator
On Fable 5, effort is the primary dial trading intelligence against latency and cost. Defaults that were right for earlier models are usually wrong here: Fable 5 at lower effort frequently beats earlier models at xhigh, so over-provisioning effort wastes money and time without adding quality.
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) — 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 |
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.
Adjustment signals
Lower effort when:
- Tasks complete correctly but take longer than the work warrants
- The session is interactive and waiting hurts more than marginal quality helps
- Output shows over-deliberation: long context-gathering before trivial actions
Raise effort when:
- First-shot correctness matters more than turnaround (one-way-door changes, unattended runs)
- The task benefits from rigorous self-verification, which higher effort does noticeably better
- A task failed at the current level in a way that looks like shallow reasoning, not missing information
Pipeline pattern
Route by task class, not by a single global setting: a triage step at low/medium that escalates hard cases to high/xhigh usually dominates any fixed choice on both cost and quality. For long agentic loops, effort composes with task budgets, an advisory token budget for the whole loop.
API shape
Set effort via output_config: {"output_config": {"effort": "low" | "medium" | "high" | "xhigh" | "max"}}. Setting high is equivalent to omitting the parameter. max_tokens is a hard limit on total output — thinking plus response text — so at higher effort leave enough headroom for extended thinking; short-response workloads may not need a change. Verify parameter names and values with the current API reference before shipping: https://platform.claude.com/docs/en/build-with-claude/effort
