Claude Sonnet 5.5 vs Claude Fable 5.1

Pyyan / Compare / Claude Sonnet 5.5 vs Claude Fable 5.1

2 of 5

Language Models · verified 29 Sept 2026

Claude Sonnet 5.5Anthropiccurrent

Claude Fable 5.1Anthropiccurrent

Add another3 slots left

Specification	Claude Sonnet 5.5	Claude Fable 5.1
Summary	Above Opus 5.5 on Terminal-Bench, at half the input price.	Same price as Fable 5, and cache reads cost a quarter of what they did.
Context	1M	1M
Input ($/Mtok)	$2	$10
Output ($/Mtok)	$10	$50
Licence	Proprietary	Proprietary
Max output	128K	128K
Parameters	Not published	Not published
Released	28 Sep 2026	1 Sep 2026
Model ID	claude-sonnet-5-5	claude-fable-5-1
Category	Language Models	Language Models
Official	Anthropic ↗	—

Highlighted rows are where these differ.

70.6% on Terminal-Bench 4.0, against 66.4% for Opus 5.5 six days earlier
1844 on GDPval-AA, level with Opus 5.5's 1846
More than 30% faster than Sonnet 5, and Anthropic says up to 30% less per task on tokens

Best for agentic coding at volume.

Matches or beats Fable 5 at low and medium effort, and pulls clear at high effort
Cache reads cut to 25% of the old price, so re-reading a long context got much cheaper
Identical model to Mythos 5.1 underneath; the difference is the safeguards

Best for coding and long-running work.