Haiku 4.5 vs Fable 5

The full span of the current lineup in one comparison

These two sit at opposite ends of the current lineup on every axis — price, capability, and thinking behaviour — and a workload genuinely torn between them is unusual; most tasks are clearly better served by one or the other rather than sitting in a genuine grey zone between them. Haiku 4.5 has no effort parameter and no thinking of its own to speak of in the same sense; Fable 5 runs extensive thinking on every single request with no way to turn it off.

Why this pairing is more useful as a sanity check than a real decision

If you find yourself genuinely uncertain between these two specifically, that's usually a sign the task itself needs re-scoping rather than a sign the models are close in suitability — a task simple enough for Haiku 4.5 to be a candidate is very unlikely to also need Fable 5's ceiling, and the reverse. Revisit what the task actually requires before treating this as a close call.

Related

See Opus 5 vs Haiku 4.5 and Opus 5 vs Fable 5 for the more commonly relevant comparisons on either side of this wide gap, and the model picker for a recommendation grounded in your actual task rather than a direct extreme-to-extreme comparison.