effort-calibrator

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

max is rarely the right answer: on most workloads it adds significant cost for small gains and can tip into overthinking. Reach for it only when xhigh has measurably fallen short.

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. At high and xhigh, set a large max_tokens — it is a hard limit on total output, thinking plus response text. Verify parameter names and values with the current API reference before shipping: https://platform.claude.com/docs/en/build-with-claude/effort