Noometry

Model comparison

Claude Fable 5.1 vs Claude Opus 4.5

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 50.5 on the Noometry Index. Claude Opus 4.5 costs 2.0× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.

Last verified . 41 shared benchmarks.

Claude Fable 5.1 Anthropic

69.0

Rank #2 Confirmed

Claude Opus 4.5 Anthropic

50.5

Rank #47 Confirmed

Summary

  • They share 41 benchmarks with published results for both. Claude Fable 5.1 scores higher in 10 categories and Claude Opus 4.5 in 0 categories; 9 gaps are clear of the uncertainty.
  • The widest gap is in math, where Claude Fable 5.1 leads 89.6 to 38.6.
  • The biggest single-benchmark swing is FrontierMath Tier 4: 87.8% for Claude Fable 5.1 and 4.9% for Claude Opus 4.5.
  • Claude Opus 4.5 is cheaper at $5 / $25 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 Opus 4.5
ProviderAnthropicAnthropic
Noometry Index69.050.5
Released2026-09-012025-11-01
WeightsProprietaryProprietary
Context window1M200K
Max output128K64K
Input $ / M tokens$10$5
Output $ / M tokens$50$25
Results tracked5269

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Category by category

Coding Claude Fable 5.1 leads

Claude Fable 5.1: 74.7 (#1), Claude Opus 4.5: 54.8 (#27)

BenchmarkClaude Fable 5.1Claude Opus 4.5
LMArena WebDev17441494
GSO88.2%26.5%
WeirdML92.9%63.7%
LMArena Coding15281504
ALE-Bench2,1431,025
SWE-bench Verified—76.7%
FrontierCode50.9%—
SWE-bench Verified (bash only)—76.8%
CursorBench51.8%—
SWE-bench Multilingual—70.7%
FrontierSWE56.3%—
SciCode63.1%—
MirrorCode73.3%—
AlgoTune—1.77

Agentic & Tool Use Claude Fable 5.1 leads

Claude Fable 5.1: 50.7 (#5), Claude Opus 4.5: 47.3 (#12)

BenchmarkClaude Fable 5.1Claude Opus 4.5
Remote Labor Index17.9%3.8%
Vending-Bench 25,4224,967
Terminal-Bench—63.1%
APEX-Agents68.6%—
Berkeley Function Calling Leaderboard—77.5%
GDPval—45.5%
τ²-bench Airline—84%
τ²-bench Banking—24.7%
τ²-bench Retail—79.6%
τ²-bench Telecom—92.3%
Cybench—82%
DeepResearch Bench—54.8%
OSWorld—66.3%
BALROG—43.5%
GDP.pdf29.6%—
LMArena Search—1180
METR Time Horizons—75%

Reasoning Claude Fable 5.1 leads

Claude Fable 5.1: 76.7 (#7), Claude Opus 4.5: 42.6 (#51)

BenchmarkClaude Fable 5.1Claude Opus 4.5
ARC-AGI-290%37.6%
NYT Connections (extended)90%52.5%
ARC-AGI-197.5%80%
Chess Puzzles47%12%
EBR-Bench57.1%14.3%
LMArena Hard Prompts15261476
Mystery Game Puzzles58%22%
DTBench97.6%89.9%
LMCA65.5%44.5%
Epoch Capabilities Index164.7150.09
SimpleBench—62%
Kagi LLM Benchmark—80.2%
CritPt31.1%—
EnigmaEval—11.9%
ForecastBench—60.7

Math Claude Fable 5.1 leads

Claude Fable 5.1: 89.6 (#4), Claude Opus 4.5: 38.6 (#132)

BenchmarkClaude Fable 5.1Claude Opus 4.5
FrontierMath (Tiers 1-3)90.2%34.4%
FrontierMath Tier 487.8%4.9%
OTIS Mock AIME 2024-2025100%86.1%
ProofBench100%36%
LMArena Math15251463
FrontierMath (Feb 2025 set)—20.7%
FrontierMath Erdős0%—
FrontierMath Tier 4 (v1)—4.2%

Knowledge Claude Fable 5.1 leads

Claude Fable 5.1: 69.6 (#6), Claude Opus 4.5: 56.5 (#44)

BenchmarkClaude Fable 5.1Claude Opus 4.5
Humanity's Last Exam46.5%25.2%
SimpleQA Verified70.8%45.7%
LMArena Expert15351487
GPQA Diamond—86%
Vectara Hallucination Rate—10.9%

Multimodal Claude Fable 5.1 leads

Claude Fable 5.1: 53.9 (#4), Claude Opus 4.5: 31.4 (#107)

BenchmarkClaude Fable 5.1Claude Opus 4.5
Furniture Assembly70%28.3%
LMArena Document15131462
LMArena Vision1318—
GeoBench—75%
VPCT—40%
Blueprint-Bench 241.9%—

Multilingual Claude Fable 5.1 leads

Claude Fable 5.1: 59.1 (#3), Claude Opus 4.5: 54.3 (#47)

BenchmarkClaude Fable 5.1Claude Opus 4.5
LMArena Non-English15071438
LMArena Chinese15861470
LMArena French15251471
LMArena German15001449
LMArena Japanese15431416
LMArena Korean15341424
LMArena Russian15211447
LMArena Spanish15161458

Instruction Following Claude Fable 5.1 leads

Claude Fable 5.1: 79.2 (#6), Claude Opus 4.5: 77.5 (#19)

BenchmarkClaude Fable 5.1Claude Opus 4.5
LMArena Instruction Following15171478

Long Context Too close to call

Claude Fable 5.1: 46.7 (#20), Claude Opus 4.5: 46.5 (#22)

BenchmarkClaude Fable 5.1Claude Opus 4.5
LMArena Longer Query15221480
CL-bench—21.1%

Writing & Preference Claude Fable 5.1 leads

Claude Fable 5.1: 79.2 (#2), Claude Opus 4.5: 68.1 (#28)

BenchmarkClaude Fable 5.1Claude Opus 4.5
LMArena Text15101451
LMArena Creative Writing15071445
EQ-Bench Creative Writing21621687
LMArena Multi-Turn14921466

Frequently asked questions

Is Claude Fable 5.1 better than Claude Opus 4.5?

Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 50.5 on the Noometry Index. Claude Opus 4.5 costs 2.0× 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 Opus 4.5?

Claude Opus 4.5 is cheaper. It lists at $5 per million input tokens and $25 per million output tokens; Claude Fable 5.1 lists at $10 and $50.

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

Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 54.8 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 Opus 4.5 share?

41 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and Claude Opus 4.5 has 69.

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