Noometry

Model comparison

Claude Fable 5.1 vs Claude Sonnet 4.5

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 44.1 on the Noometry Index. Claude Sonnet 4.5 costs 3.3× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.

Last verified . 42 shared benchmarks.

Claude Fable 5.1 Anthropic

69.0

Rank #2 Confirmed

Claude Sonnet 4.5 Anthropic

44.1

Rank #81 Confirmed

Summary

  • They share 42 benchmarks with published results for both. Claude Fable 5.1 scores higher in 10 categories and Claude Sonnet 4.5 in 0 categories; 10 gaps are clear of the uncertainty.
  • The widest gap is in math, where Claude Fable 5.1 leads 89.6 to 32.3.
  • The biggest single-benchmark swing is FrontierMath Tier 4: 87.8% for Claude Fable 5.1 and 2.4% for Claude Sonnet 4.5.
  • Claude Sonnet 4.5 is cheaper at $3 / $15 per million input/output tokens, against $10 / $50 for Claude Fable 5.1.
  • Claude Fable 5.1 accepts more context: 1M tokens versus 200K.

Side by side

Claude Fable 5.1Claude Sonnet 4.5
ProviderAnthropicAnthropic
Noometry Index69.044.1
Released2026-09-012025-09-29
WeightsProprietaryProprietary
Context window1M200K
Max output128K64K
Input $ / M tokens$10$3
Output $ / M tokens$50$15
Results tracked5273

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Category by category

Coding Claude Fable 5.1 leads

Claude Fable 5.1: 74.7 (#1), Claude Sonnet 4.5: 47.3 (#61)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena WebDev17441393
SciCode63.1%44.7%
GSO88.2%14.7%
WeirdML92.9%47.7%
LMArena Coding15281489
ALE-Bench2,143796.15
SWE-bench Verified—71.3%
FrontierCode50.9%—
SWE-bench Verified (bash only)—71.4%
CursorBench51.8%—
SWE-bench Multilingual—67%
FrontierSWE56.3%—
MirrorCode73.3%—
AlgoTune—1.52

Agentic & Tool Use Claude Fable 5.1 leads

Claude Fable 5.1: 50.7 (#5), Claude Sonnet 4.5: 38.3 (#32)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
Remote Labor Index17.9%2.1%
Vending-Bench 25,4223,839
Terminal-Bench—46.5%
APEX-Agents68.6%—
Berkeley Function Calling Leaderboard—73.2%
GDPval—42.5%
τ²-bench Airline—72%
τ²-bench Banking—25.3%
τ²-bench Retail—72.4%
τ²-bench Telecom—84.9%
Cybench—60%
DeepResearch Bench—52.6%
OSWorld—62.9%
GDP.pdf29.6%—
LMArena Search—1159
METR Time Horizons—67.4%

Reasoning Claude Fable 5.1 leads

Claude Fable 5.1: 76.7 (#7), Claude Sonnet 4.5: 26.9 (#125)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
ARC-AGI-290%13.6%
NYT Connections (extended)90%37.3%
ARC-AGI-197.5%63.7%
CritPt31.1%1.1%
Chess Puzzles47%12%
EBR-Bench57.1%2.4%
LMArena Hard Prompts15261462
Mystery Game Puzzles58%17%
DTBench97.6%83.2%
LMCA65.5%38.8%
Epoch Capabilities Index164.7146.84
SimpleBench—54.3%
Kagi LLM Benchmark—57.9%
EnigmaEval—6%
ForecastBench—61.9

Math Claude Fable 5.1 leads

Claude Fable 5.1: 89.6 (#4), Claude Sonnet 4.5: 32.3 (#216)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
FrontierMath (Tiers 1-3)90.2%23.9%
FrontierMath Tier 487.8%2.4%
OTIS Mock AIME 2024-2025100%77.8%
ProofBench100%19%
LMArena Math15251449
Omni-MATH—55.3%
MATH Level 5—97.7%
FrontierMath (Feb 2025 set)—15.2%
FrontierMath Erdős0%—
FrontierMath Tier 4 (v1)—4.2%

Knowledge Claude Fable 5.1 leads

Claude Fable 5.1: 69.6 (#6), Claude Sonnet 4.5: 48.4 (#76)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
Humanity's Last Exam46.5%13.7%
SimpleQA Verified70.8%30.7%
LMArena Expert15351482
GPQA Diamond—82.3%
MMLU-Pro—86.9%
Vectara Hallucination Rate—12%
GPQA (HELM)—68.6%

Multimodal Claude Fable 5.1 leads

Claude Fable 5.1: 53.9 (#4), Claude Sonnet 4.5: 34.8 (#89)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena Document15131450
LMArena Vision1318—
VPCT—39.8%
Blueprint-Bench 241.9%—
Furniture Assembly70%—

Multilingual Claude Fable 5.1 leads

Claude Fable 5.1: 59.1 (#3), Claude Sonnet 4.5: 53.4 (#69)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena Non-English15071425
LMArena Chinese15861459
LMArena French15251458
LMArena German15001427
LMArena Japanese15431390
LMArena Korean15341403
LMArena Russian15211437
LMArena Spanish15161457

Instruction Following Claude Fable 5.1 leads

Claude Fable 5.1: 79.2 (#6), Claude Sonnet 4.5: 75.0 (#78)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena Instruction Following15171459
IFEval—85%

Long Context Claude Fable 5.1 leads

Claude Fable 5.1: 46.7 (#20), Claude Sonnet 4.5: 45.2 (#46)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena Longer Query15221476

Writing & Preference Claude Fable 5.1 leads

Claude Fable 5.1: 79.2 (#2), Claude Sonnet 4.5: 66.5 (#34)

BenchmarkClaude Fable 5.1Claude Sonnet 4.5
LMArena Text15101439
LMArena Creative Writing15071442
EQ-Bench Creative Writing21621678
LMArena Multi-Turn14921465
WildBench—85.4%

Frequently asked questions

Is Claude Fable 5.1 better than Claude Sonnet 4.5?

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 44.1 on the Noometry Index. Claude Sonnet 4.5 costs 3.3× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.

Which is cheaper, Claude Fable 5.1 or Claude Sonnet 4.5?

Claude Sonnet 4.5 is cheaper. It lists at $3 per million input tokens and $15 per million output tokens; Claude Fable 5.1 lists at $10 and $50.

Is Claude Fable 5.1 or Claude Sonnet 4.5 better for coding?

Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 47.3 in the Noometry coding category.

Which has the bigger context window?

Claude Fable 5.1 does, with 1M tokens against 200K.

How many benchmarks do Claude Fable 5.1 and Claude Sonnet 4.5 share?

42 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and Claude Sonnet 4.5 has 73.

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