Fable 5's combination of frontier pricing and agentic fan-out means per-step model routing, token budgets, and cost-per-task observability shift from optional optimizations to required components of any production agent orchestration layer.
The post, backed by Terminal-Bench 2.0 and Harness-Bench data, makes the case that harness engineering is a first-class performance variable — meaning benchmark results reported at the model level alone may be systematically misleading.