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Claude Fable 5.1 vs Claude Sonnet 5.5

Updated October 20, 2026. 89 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace Claude Fable 5.1 Replace Claude Sonnet 5.5
Claude Fable 5.1Anthropic
Coding
89.1
Overall
53.4
Output $/M
$50.00
58
Claude Sonnet 5.5Anthropic
Coding
88.9
Overall
56.0
Output $/M
$10.00
29
vs boards won of 89 shared, 2 tied

Decision reading

Claude Fable 5.1 and Claude Sonnet 5.5 are level for coding, 89.1 against 88.9 on the Vibe Coding Index, so price and context decide.

Pick Claude Sonnet 5.5 when output tokens cost 5.0x less, or when what matters is LMArena WebDev or Terminal-Bench 4 (Vals AI), where it leads. Pick Claude Fable 5.1 when what matters is LiveBench coding or ProgramBench (Vals AI), where it leads.

Model AClaude Fable 5.1Anthropic89.1/1002 independent benchmarksNo cost per solved taskModel BClaude Sonnet 5.5Anthropic88.9/1002 independent benchmarksNo cost per solved task
Shared results
89
Claude Fable 5.1 only
35
Claude Sonnet 5.5 only
5
Like-for-like categories
8 of 9

Shared results can support a head-to-head reading. Results only one model has describe coverage, not superiority.

Which one for your work

Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.

At a glance

Coding index
Claude Fable 5.1 89.1 from 2 benchmarks, Claude Sonnet 5.5 88.9 from 2 benchmarks.
Widest category
Knowledge, 9.3 points apart on average over 6 shared benchmarks.
Widest single gap
Vending-Bench 2: Claude Fable 5.1 $5,422 against Claude Sonnet 5.5 $11,165, 35.9 points apart on a 0 to 100 scale.
Output price
Claude Fable 5.1 $50.00 against Claude Sonnet 5.5 $10.00 per million output tokens, 5.0x apart.
Context window
Both take 1M tokens.

Benchmark by benchmark

First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.

Boards won, where both have a result
CategoryClaude Fable 5.1BarsClaude Sonnet 5.5Ties
Coding109
Intelligence11
Agentic work76
Reasoning83
Math402 ties
Knowledge60
Web design07
General223
All shared boards58292 ties
CodingLike-for-likeFour of these boards feed the Vibe Coding Index109
Coding benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
LiveBench coding97.7%94.7%Claude Fable 5.1
LMArena WebDev17431768Claude Sonnet 5.5
AA Coding Index81.6Not measuredOnly Claude Fable 5.1 measured
LiveCodeBench (Vals AI)90.5%Not measuredOnly Claude Fable 5.1 measured
Terminal-Bench 4 (Vals AI)58.1%64.1%Claude Sonnet 5.5
Vibe Code Bench (Vals AI)90.3%92.4%Claude Sonnet 5.5
Code migration (Vals AI)54.6%69.8%Claude Sonnet 5.5
ProgramBench (Vals AI)7.0%6.5%Claude Fable 5.1
IOI (Vals AI)90.8%83.1%Claude Fable 5.1
Terminal-Bench 2.1 (Vals AI)85.0%83.2%Claude Fable 5.1
SWE-bench Multimodal (Vals AI)61.3%58.3%Claude Fable 5.1
Vibe Code Bench 1-100 (Vals AI)28.0%Not measuredOnly Claude Fable 5.1 measured
SkillsBench (Vals AI)61.5%Not measuredOnly Claude Fable 5.1 measured
CyberBench (Vals AI)70.4%59.6%Claude Fable 5.1
SciCode63.1%61.0%Claude Fable 5.1
FrontierCode50.9%52.1%Claude Sonnet 5.5
FrontierSWE56.3%61.9%Claude Sonnet 5.5
GSO-Bench88.2%Not measuredOnly Claude Fable 5.1 measured
WeirdML92.9%Not measuredOnly Claude Fable 5.1 measured
MirrorCode73.3%Not measuredOnly Claude Fable 5.1 measured
ALE-Bench2143.21819.1Claude Fable 5.1
LMArena Text: coding15311513Claude Fable 5.1
LMArena Text: software and IT15291501Claude Fable 5.1
LMArena WebDev: React17921817Claude Sonnet 5.5
LMArena WebDev: HTML16841741Claude Sonnet 5.5
LMArena WebDev: from an image17221737Claude Sonnet 5.5
Neither model has a result on the other 12 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index11
Intelligence benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
AA Intelligence Index53.456.0Claude Sonnet 5.5
Epoch Capabilities Index164.7164.4Claude Fable 5.1
Agentic workLike-for-likePublic boards, shown as published, kept out of the index76
Agentic work benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
AA Agentic Index57.9Not measuredOnly Claude Fable 5.1 measured
Design Arena: agents building web apps1318Not measuredOnly Claude Fable 5.1 measured
Design Arena: agents building full-stack apps1326Not measuredOnly Claude Fable 5.1 measured
Design Arena: agents building mobile apps12661272Claude Sonnet 5.5
Design Arena: agents building Godot games1327Not measuredOnly Claude Fable 5.1 measured
Design Arena: PowerPoint slides1328Not measuredOnly Claude Fable 5.1 measured
LiveBench research82.0%83.6%Claude Sonnet 5.5
LiveBench browser100.0%84.0%Claude Fable 5.1
LiveBench long agentic80.8%78.8%Claude Fable 5.1
SREBench (Vals AI)22.9%30.1%Claude Sonnet 5.5
Finance Agent (Vals AI)58.9%58.1%Claude Fable 5.1
Tax Agent Bench (Vals AI)49.2%42.0%Claude Fable 5.1
Legal Research Bench (Vals AI)55.3%48.1%Claude Fable 5.1
Harvey's Legal Agent Benchmark (Vals AI)Not measured10.4%Only Claude Sonnet 5.5 measured
Excel Modeling Benchmark (Vals AI)76.7%75.7%Claude Fable 5.1
BioMysteryBench (Vals AI)Not measured81.1%Only Claude Sonnet 5.5 measured
Terminal-Bench-Science (Vals AI)40.0%47.1%Claude Sonnet 5.5
Vals Science IndexNot measured59.1%Only Claude Sonnet 5.5 measured
Time Horizon Index (Vals AI)63.3%Not measuredOnly Claude Fable 5.1 measured
CUA-bench (Vals AI)13.2%Not measuredOnly Claude Fable 5.1 measured
Robo-bench (Vals AI)5.8%Not measuredOnly Claude Fable 5.1 measured
APEX-Agents68.6%75.5%Claude Sonnet 5.5
Remote Labor Index17.9%Not measuredOnly Claude Fable 5.1 measured
SpireClimb2.0%1.3%Claude Fable 5.1
Vending-Bench 2$5,422$11,165Claude Sonnet 5.5
LMArena Search1246Not measuredOnly Claude Fable 5.1 measured
Neither model has a result on the other 13 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index83
Reasoning benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
GPQA Diamond93.4%Not measuredOnly Claude Fable 5.1 measured
LiveBench reasoning91.7%91.6%Claude Fable 5.1
MysteryMechanism (Vals AI)47.8%49.1%Claude Sonnet 5.5
MMMU Pro (Vals AI)90.6%Not measuredOnly Claude Fable 5.1 measured
GPQA Diamond (Artificial Analysis run)93.7%Not measuredOnly Claude Fable 5.1 measured
Humanity's Last Exam (Artificial Analysis run)59.1%55.0%Claude Fable 5.1
GPQA Diamond (Epoch AI run)Not measured95.6%Only Claude Sonnet 5.5 measured
ARC-AGI97.5%Not measuredOnly Claude Fable 5.1 measured
ARC-AGI-290.0%Not measuredOnly Claude Fable 5.1 measured
Humanity's Last Exam46.5%46.1%Claude Fable 5.1
Chess puzzles48.0%59.0%Claude Sonnet 5.5
Mystery game puzzles58.0%65.0%Claude Sonnet 5.5
EBR-bench57.1%Not measuredOnly Claude Fable 5.1 measured
LMArena Text: hard prompts15261493Claude Fable 5.1
LMArena Text: expert15401532Claude Fable 5.1
LMArena Text: hard prompts in English15211503Claude Fable 5.1
LMArena Vision: diagrams13431329Claude Fable 5.1
LMArena Vision: homework13451331Claude Fable 5.1
Neither model has a result on the other 3 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index40
Math benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
OTIS Mock AIME100.0%100.0%Tie
FrontierMath, tiers 1 to 390.2%88.8%Claude Fable 5.1
FrontierMath, tier 487.8%80.5%Claude Fable 5.1
ProofBench100.0%100.0%Tie
LMArena Text: math15281499Claude Fable 5.1
LMArena Text: mathematical work15371506Claude Fable 5.1
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index60
Knowledge benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
MMLU Pro92.4%Not measuredOnly Claude Fable 5.1 measured
LegalBench (Vals AI)88.5%Not measuredOnly Claude Fable 5.1 measured
TaxEval (Vals AI)76.0%Not measuredOnly Claude Fable 5.1 measured
MortgageTax (Vals AI)70.8%Not measuredOnly Claude Fable 5.1 measured
MedCode (Vals AI)53.5%52.9%Claude Fable 5.1
SimpleQA Verified70.8%46.5%Claude Fable 5.1
LMArena Text: science15321479Claude Fable 5.1
LMArena Text: medicine and healthcare15301456Claude Fable 5.1
LMArena Text: legal and government15111485Claude Fable 5.1
LMArena Text: business and finance14931460Claude Fable 5.1
Neither model has a result on the other 7 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index07
Web design benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
Design Arena: websites13131326Claude Sonnet 5.5
Design Arena: UI components13391372Claude Sonnet 5.5
Design Arena: game dev13811472Claude Sonnet 5.5
Design Arena: data viz13441387Claude Sonnet 5.5
Design Arena: 3D13931458Claude Sonnet 5.5
Design Arena: all code categories13361365Claude Sonnet 5.5
Design Arena: SVG1300Not measuredOnly Claude Fable 5.1 measured
Design Arena: ASCII art1323Not measuredOnly Claude Fable 5.1 measured
LiveBench design83.4%85.0%Claude Sonnet 5.5
GeneralLike-for-likePublic boards, shown as published, kept out of the index223
General benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
Vals IndexNot measured70.8%Only Claude Sonnet 5.5 measured
LiveBench data analysis80.3%59.5%Claude Fable 5.1
Public Benefits Bench (Vals AI)74.9%67.2%Claude Fable 5.1
SAGE (Vals AI)48.5%51.8%Claude Sonnet 5.5
MedScribe (Vals AI)91.3%91.1%Claude Fable 5.1
Long context reasoning (AA-LCR)85.3%82.7%Claude Fable 5.1
DTBench97.6%97.3%Claude Fable 5.1
LMCA65.5%68.3%Claude Sonnet 5.5
Furniture assembly70.0%75.0%Claude Sonnet 5.5
LMArena Text15121470Claude Fable 5.1
LMArena Text: instruction following15171488Claude Fable 5.1
LMArena Text: creative writing15081467Claude Fable 5.1
LMArena Vision13191287Claude Fable 5.1
LMArena Text: English15051485Claude Fable 5.1
LMArena Text: non-English15071454Claude Fable 5.1
LMArena Text: Chinese15861537Claude Fable 5.1
LMArena Text: German1502Not measuredOnly Claude Fable 5.1 measured
LMArena Text: Japanese1560Not measuredOnly Claude Fable 5.1 measured
LMArena Text: Korean1521Not measuredOnly Claude Fable 5.1 measured
LMArena Text: French15271497Claude Fable 5.1
LMArena Text: Spanish15211450Claude Fable 5.1
LMArena Text: Russian15191445Claude Fable 5.1
LMArena Text: Polish1524Not measuredOnly Claude Fable 5.1 measured
LMArena Text: multi-turn14931463Claude Fable 5.1
LMArena Text: longer queries15231494Claude Fable 5.1
LMArena Text: writing and language15091472Claude Fable 5.1
LMArena Text: entertainment and media14951458Claude Fable 5.1
LMArena Vision: English13131289Claude Fable 5.1
LMArena Vision: Chinese1391Not measuredOnly Claude Fable 5.1 measured
LMArena Vision: reading text13271297Claude Fable 5.1
LMArena Vision: humor1318Not measuredOnly Claude Fable 5.1 measured
LMArena Vision: creative writing13301242Claude Fable 5.1
Neither model has a result on the other 14 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for Claude Fable 5.1 and Claude Sonnet 5.5
BenchmarkClaude Fable 5.1Claude Sonnet 5.5Leader
Neither model has a result on 5 boards here

What each workload costs

Three fixed token mixes at each model's listed price, so per-token rates become a bill.

Chat turn

1K input + 500 output tokens

Claude Fable 5.1$0.035Fits in one request
Claude Sonnet 5.5$0.0070Fits in one request

Claude Sonnet 5.5 costs less

Repository review

50K input + 3K output tokens

Claude Fable 5.1$0.650Fits in one request
Claude Sonnet 5.5$0.130Fits in one request

Claude Sonnet 5.5 costs less

Agent loop

200K input + 10K output tokens

Claude Fable 5.1$2.50Fits in one request
Claude Sonnet 5.5$0.500Fits in one request

Claude Sonnet 5.5 costs less

Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.

Specification differences

The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.

Specifications of Claude Fable 5.1 and Claude Sonnet 5.5
SpecificationAnthropic Claude Fable 5.1Anthropic Claude Sonnet 5.5
MakerAnthropicAnthropic
WeightsNo public weights listedNo public weights listed
ReleasedSeptember 1, 2026September 28, 2026
Context window1M1M
Input $/Mtok$10.00$2.00
Output $/Mtok$50.00$10.00
Coding index89.188.9
Independent measurements behind it22
Cost per solved taskNot computableNot computable
SourceOpenRouter listingOpenRouter listing

Questions

Is Claude Fable 5.1 better than Claude Sonnet 5.5 for coding?

Claude Fable 5.1 and Claude Sonnet 5.5 are level for coding, 89.1 against 88.9 on the Vibe Coding Index, so price and context decide. Pick Claude Sonnet 5.5 when output tokens cost 5.0x less, or when what matters is LMArena WebDev or Terminal-Bench 4 (Vals AI), where it leads. Pick Claude Fable 5.1 when what matters is LiveBench coding or ProgramBench (Vals AI), where it leads.

Which is cheaper, Claude Fable 5.1 or Claude Sonnet 5.5?

Claude Fable 5.1 costs $10.00 per million input tokens and $50.00 per million output tokens; Claude Sonnet 5.5 costs $2.00 and $10.00. Cost per solved task is known for neither of them.

Which has the bigger context window, Claude Fable 5.1 or Claude Sonnet 5.5?

Neither: both take 1M tokens.

How many benchmarks is the Claude Fable 5.1 vs Claude Sonnet 5.5 comparison based on?

89 benchmarks have a result for both models as of October 20, 2026. Claude Fable 5.1's coding index rests on 2 independent benchmarks and Claude Sonnet 5.5's on 2. Where only one model has a result, the page says so instead of naming a winner.

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<p style="font:13px/1.4 sans-serif;margin:6px 0 0">Source: <a href="https://llmbenchmark.ai/compare/claude-fable-5-1-vs-claude-sonnet-5-5">LLMBenchmark.ai, Claude Fable 5.1 vs Claude Sonnet 5.5</a></p>