Head-to-head comparison

Claude Sonnet 5.5 vs. Claude Fable 5.1

Compare published benchmark results from matching versions and cohorts, API pricing, and technical specifications. Any documented test setup differences remain visible.

shared result series: 20
distinct benchmarks: 20
latest retrieval: 2026-09-29

First modelSecond model

Specifications

General specifications

Release date, availability, context window, architecture, and published parameter counts at a glance. Undisclosed details remain marked as unavailable.

Specifications for Claude Sonnet 5.5 and Claude Fable 5.1
Attribute	Claude Sonnet 5.5	Claude Fable 5.1
Provider	Anthropic	Anthropic
Released	Sep 28, 2026	Sep 1, 2026
Availability	Active	Active
Model type	Proprietary	Proprietary
Parameters	Not published	Not published
Architecture	Not published	Not published
Context window	1,000,000 tokens	1,000,000 tokens
Knowledge cutoff	June 2026	June 2026
Technical sources	Model	Model

Pricing

API pricing compared

The table compares official standard API rates per 1M tokens, including published cache pricing. Batch, fast, priority, regional surcharges, tool calls, and cloud platform pricing are excluded.

API pricing for Claude Sonnet 5.5 and Claude Fable 5.1
Price type	Claude Sonnet 5.5	Claude Fable 5.1
API input	$2	$10
API output	$10	$50
Cache read	$0.2	$0.25
Cache write (5 min.)	$2.5	$12.5
Cache write (1 hr.)	$4	$20
Price verified	09/28/2026 Source	09/22/2026 Source

Claude Sonnet 5.5Claude Fable 5.1

API inputUSD per 1M tokens, base tier

Claude Sonnet 5.5$2

Claude Fable 5.1$10

API outputUSD per 1M tokens, base tier

Claude Sonnet 5.5$10

Claude Fable 5.1$50

Cache readUSD per 1M tokens, base tier

Claude Sonnet 5.5$0.2

Claude Fable 5.1$0.25

Key to the marks:better valuebetter, but not conclusivetie

Pricing by provider

Direct developer pricing and provider endpoint tariffs routed through OpenRouter are listed separately. Prices are in USD per 1M tokens. Context-dependent direct tiers plus regional, Flex, Priority, and other OpenRouter tariffs remain individually identifiable.

Provider pricing for Claude Sonnet 5.5 and Claude Fable 5.1
Model	Provider	Purchase route and tariff	Input per 1M tokens	Output per 1M tokens	Source
Claude Sonnet 5.5	Anthropic	Direct from developerStandard API	Lowest listed price: $2	Lowest listed price: $10	Source09/28/2026
	Amazon Bedrock	Via OpenRouteramazon-bedrock	Lowest listed price: $2	Lowest listed price: $10	Source10/07/2026
	Anthropic	Via OpenRouteranthropic	Lowest listed price: $2	Lowest listed price: $10	Source10/07/2026
	Azure	Via OpenRouterazure/global	Lowest listed price: $2	Lowest listed price: $10	Source10/07/2026
	Azure	Via OpenRouterazure/us	$2.2	$11	Source10/07/2026
	Claude Platform on AWS	Via OpenRouterclaude-on-aws	Lowest listed price: $2	Lowest listed price: $10	Source10/07/2026
	Google	Via OpenRoutergoogle-vertex/europe	$2.2	$11	Source10/07/2026
	Google	Via OpenRoutergoogle-vertex/global	Lowest listed price: $2	Lowest listed price: $10	Source10/07/2026
	Google	Via OpenRoutergoogle-vertex/us	$2.2	$11	Source10/07/2026
Claude Fable 5.1	Anthropic	Direct from developerStandard API	Lowest listed price: $10	Lowest listed price: $50	Source09/22/2026
	Amazon Bedrock	Via OpenRouteramazon-bedrock	Lowest listed price: $10	Lowest listed price: $50	Source10/07/2026
	Anthropic	Via OpenRouteranthropic	Lowest listed price: $10	Lowest listed price: $50	Source10/07/2026
	Azure	Via OpenRouterazure	Lowest listed price: $10	Lowest listed price: $50	Source10/07/2026
	Google	Via OpenRoutergoogle-vertex/global	Lowest listed price: $10	Lowest listed price: $50	Source10/07/2026

Performance

Shared benchmarks

Only published results with the same benchmark version, task, metric, and comparison cohort are paired. Different reasoning levels, agents, harnesses, or output limits appear directly in the table.

Capability profile from matched benchmarks

Each axis averages directly matched benchmark families. A value of 100 means the stronger value within this pair, not a universal quality score.

Claude Sonnet 5.5

Claude Fable 5.1

Coding: 97.9 / 92.3 (4 benchmark families)

Mathematics: 100 / 100 (1 benchmark family)

Finance: 97.3 / 100 (3 benchmark families)

Legal: 65.4 / 100 (2 benchmark families)

Agentic tasks: 97.8 / 100 (1 benchmark family)

Productivity: 89.7 / 100 (1 benchmark family)

Cybersecurity: 84.6 / 100 (1 benchmark family)

Health: 99.3 / 100 (2 benchmark families)

20 matched rows from 19 benchmark families were considered. The radar shows 8 of 11 comparable categories.

Claude Sonnet 5.5Claude Fable 5.1

Code MigrationOverall. Higher is better. No documented setup difference

Claude Sonnet 5.569.825 %

Claude Fable 5.154.607 %

CyberBench v1.1Overall. Higher is better. No documented setup difference

Claude Sonnet 5.559.584 %

Claude Fable 5.170.416 %

EMBOverall. Higher is better. No documented setup difference

Claude Sonnet 5.575.713 %

Claude Fable 5.176.67 %

Finance Agent (v2)Overall. Higher is better. No documented setup difference

Claude Sonnet 5.558.103 %

Claude Fable 5.158.877 %

Harvey's Legal Agent BenchmarkOverall · Task fully resolved. Higher is better. No documented setup difference

Claude Sonnet 5.52.917 %

Claude Fable 5.16.667 %

IOIOverall. Higher is better. No documented setup difference

Claude Sonnet 5.583.056 %

Claude Fable 5.190.778 %

Legal Research BenchOverall · All-pass. Higher is better. No documented setup difference

Claude Sonnet 5.548.077 %

Claude Fable 5.155.288 %

MedCodeOverall. Higher is better. No documented setup difference

Claude Sonnet 5.552.92 %

Claude Fable 5.153.509 %

MedScribeOverall. Higher is better. No documented setup difference

Claude Sonnet 5.591.101 %

Claude Fable 5.191.294 %

MysteryMechanismOverall. Higher is better. No documented setup difference

Claude Sonnet 5.549.099 %

Claude Fable 5.147.748 %

ProofBenchOverall. Higher is better. No documented setup difference

Claude Sonnet 5.5100 %

Claude Fable 5.1100 %

Public Benefits Bench v1.1Overall. Higher is better. No documented setup difference

Claude Sonnet 5.567.185 %

Claude Fable 5.174.899 %

Key to the marks:better valuebetter, but not conclusivetie

Benchmark scores for Claude Sonnet 5.5 and Claude Fable 5.1
Benchmark and task	Claude Sonnet 5.5	Claude Fable 5.1	Source
Code MigrationOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	Winner69.825 %	54.607 %	Vals AI Source details Data as of: 09/27/2026
CyberBench v1.1Overall Test details No documented difference in the test setupVersion: 1.1Metric: accuracyScoring: Higher is better	59.584 %	Winner70.416 %	Vals AI Source details Data as of: 09/27/2026
EMBOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	75.713 %	Winner76.67 %	Vals AI Source details Data as of: 09/27/2026
Finance Agent (v2)Overall Test details No documented difference in the test setupVersion: 2Metric: accuracyScoring: Higher is better	58.103 %	Winner58.877 %	Vals AI Source details Data as of: 09/27/2026
Harvey's Legal Agent BenchmarkOverall · Task fully resolved Test details No documented difference in the test setupVersion: 1Metric: task resolution rateScoring: Higher is better	2.917 %	Winner6.667 %	Vals AI Source details Data as of: 09/27/2026
IOIOverall Test details No documented difference in the test setupVersion: 2Metric: accuracyScoring: Higher is better	83.056 %	Winner90.778 %	Vals AI Source details Data as of: 09/27/2026
Legal Research BenchOverall · All-pass Test details No documented difference in the test setupVersion: 1Metric: all-pass rateScoring: Higher is better	48.077 %	Winner55.288 %	Vals AI Source details Data as of: 09/27/2026
MedCodeOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	52.92 %	Winner53.509 %	Vals AI Source details Data as of: 09/26/2026
MedScribeOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	91.101 %	Winner91.294 %	Vals AI Source details Data as of: 09/26/2026
MysteryMechanismOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	Winner49.099 %	47.748 %	Vals AI Source details Data as of: 09/27/2026
ProofBenchOverall Test details No documented difference in the test setupVersion: 1.1Metric: accuracyScoring: Higher is better	Tie100 %	Tie100 %	Vals AI Source details Data as of: 09/28/2026
Public Benefits Bench v1.1Overall Test details No documented difference in the test setupVersion: 1.1Metric: accuracyScoring: Higher is better	67.185 %	Winner74.899 %	Vals AI Source details Data as of: 09/27/2026
SAGEOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	Winner51.772 %	48.526 %	Vals AI Source details Data as of: 09/26/2026
SRE BenchOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	Winner30.153 %	22.901 %	Vals AI Source details Data as of: 09/27/2026
Tax Agent BenchOverall Test details No documented difference in the test setupVersion: 1Metric: accuracyScoring: Higher is better	73.395 %	Winner77.642 %	Vals AI Source details Data as of: 09/27/2026
Terminal-Bench 2.1Overall Test details No documented difference in the test setupVersion: 2.1Metric: accuracyScoring: Higher is better	83.146 %	Winner85.019 %	Vals AI Source details Data as of: 09/27/2026
Terminal-Bench 4.0Overall Test details No documented difference in the test setupVersion: 4.0Metric: accuracyScoring: Higher is better	Winner53.03 %	49.495 %	Vals AI Source details Data as of: 09/27/2026
Terminal-Bench ScienceOverall Test details No documented difference in the test setupVersion: 0.1Metric: accuracyScoring: Higher is better	Winner38.571 %	34.286 %	Vals AI Source details Data as of: 09/27/2026
Vals IndexOverall Test details No documented difference in the test setupVersion: 2Metric: weighted index scoreScoring: Higher is better	Winner69.219 %	68.825 %	Vals AI Source details Data as of: 09/27/2026
Vibe Code Bench v1.1Overall Test details No documented difference in the test setupVersion: 1.1Metric: accuracyScoring: Higher is betterSettings: Harness: OpenHands	Winner92.392 %	90.263 %	Vals AI Source details Data as of: 09/27/2026
Key to the marks:better valuebetter, but not conclusivetie

Our model tests

Our tests

Compare how the models respond to the same prompt. Each test shows the latest attempt, with no subsequent fixes to the generated code. Earlier runs remain available in the test details. These results do not contribute to an overall score.

Pelican on a bicycle

A community classic for free-form SVG drawing.

Claude Sonnet 5.5

Reasoning (requested): high

Current attempt

Run date: 1 Oct 2026
API provider: openrouter
Requested API model: anthropic/claude-sonnet-5.5
API model reported in response: anthropic/claude-sonnet-5.5
Reasoning setting: high
Pinned endpoint: Anthropic | anthropic/claude-sonnet-5.5-20260928
Temperature: Provider default
Token limit including reasoning: 8,192 tokens
Test protocol: community-visual-tests-v1
Technical checks: Passed, not a quality rating
Response time: 28.2 s

Visually reviewed. This individual test does not establish overall model quality.

Claude Fable 5.1

Reasoning (requested): high

Current attempt

Run date: 7 Sept 2026
API provider: openrouter
Requested API model: anthropic/claude-fable-5.1
API model reported in response: anthropic/claude-fable-5.1
Reasoning setting: high
Pinned endpoint: Anthropic | anthropic/claude-fable-5.1-20260831
Temperature: Provider default
Token limit including reasoning: 8,192 tokens
Test protocol: community-visual-tests-v1
Technical checks: Passed, not a quality rating
Response time: 27 s

Visually reviewed. This individual test does not establish overall model quality.

Prompt and test conditions

Generate an SVG of a pelican riding a bicycle

Token limit including reasoning: 8,192 tokens

Task origin (Simon Willison)

How to read this comparison

Winning one benchmark is not an overall verdict

Your workload, budget, and required context length matter most. A coding benchmark says little about visual understanding or agent performance.

The standard price table uses direct developer rates. The provider comparison labels OpenRouter endpoints, regions, and special tariffs separately.

Every result links to its measurement source and retrieval date. Labels distinguish vendor reports, official benchmark leaderboards, and independent evaluations. Disputed or archived results are excluded.

More matchups

Compare Claude Sonnet 5.5 and Claude Fable 5.1 with other leading models using the same data and benchmark logic.

View the complete LLM comparison