> Claude Sonnet 5.5 vs Claude Fable 5.1: index scores 193 and 192 (GPT-4 = 100), API prices, context windows and results on the same independent tests, side by side.

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# Compare

Side by side on the same independent tests, with price and context. The link in your address bar shares this exact comparison.

[Claude Sonnet 5.5](https://themodelindex.org/models/claude-sonnet-5-5/)

[Claude Fable 5.1](https://themodelindex.org/models/claude-fable-5-1/)

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Next to Claude Sonnet 5.5

Best open model, measured

Kimi K3

Closest rival, another lab

GPT-6 Astra

The version it replaced

Claude Sonnet 5

Where it started

GPT-4

Presets

Best open vs best closed (measured)

Today vs GPT-4 (2023)

Top three labs

US vs China, best of each

[Claude Sonnet 5.5](https://themodelindex.org/models/claude-sonnet-5-5/)

193

182–205

Weights

Closed

Released

Sep 2026

Price in / out

$2.0 / $10

Context

1M

Core tests taken

3 of 8

[Claude Fable 5.1](https://themodelindex.org/models/claude-fable-5-1/)

192

181–203

Weights

Closed

Released

Sep 2026

Price in / out

$10 / $50

Context

1M

Core tests taken

4 of 8

Claude Sonnet 5.5 and Claude Fable 5.1 are too close to call (1 points apart, within the uncertainty), ahead on 1 of 2 shared core tests, and costs 5.0× less.

## Test by test · independent results · Epoch AI

Claude Sonnet 5.5

Claude Fable 5.1

_Chart: Test results for the selected models_

Only tests that at least two of these models have taken. Bold rows are the core tests shown on every profile; all of these results inform the index score. Task length (METR) is listed below the chart because it is a duration, not a percentage.

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Source: https://themodelindex.org/compare/claude-sonnet-5-5-vs-claude-fable-5-1/ · The Model Index · data as of 2026-10-01