From the source

Fable 5.1

Claude Fable 5.1 now powers Amp's ultra mode at 35% lower cost.

Model update

Amp released Fable 5.1, which powers its ultra mode, replacing Fable 5.

The model is better at writing, long-horizon tasks, and following instructions mid-task, and costs less to run.

From the source
Claude Fable 5.1 now powers Amp's ultra mode, replacing Fable 5.
ampcode.com

Announced: 01 Sep 2026
First seen by forck: 03 Sep 2026 14:35 UTC (≥38h after)
Pricing: ultra threads about 35% cheaper; cache reads 75% cheaper than Fable 5

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