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Claude Fable 5.1 vs Gemini 3.8 Flash

Claude Fable 5.1 leads Gemini 3.8 Flash on coding, 84.2 to 61.6 on the Vibe Coding Index, and Gemini 3.8 Flash costs 13.3x less per output token ($3.75 vs $50.00 per million). Updated October 22, 2026; 118 benchmarks have a result for both.

Replace Claude Fable 5.1 Replace Gemini 3.8 Flash
Claude Fable 5.1Anthropic
Coding
84.2
Overall
84.7
Output $/M
$50.00
104
Gemini 3.8 FlashGoogle
Coding
61.6
Overall
69.0
Output $/M
$3.75
14
vs boards won of 118 shared

Claude Fable 5.1 or Gemini 3.8 Flash: which to pick

Pick Claude Fable 5.1 for coding: it scores 84.2 on the Vibe Coding Index against 61.6 for Gemini 3.8 Flash, though on 5 benchmarks against 6.

Pick Gemini 3.8 Flash for output tokens 13.3x cheaper ($3.75 vs $50.00 per million) and a larger context window (1.05M against 1M tokens).

Model AClaude Fable 5.1Anthropic84.2/1005 independent benchmarksNo cost per solved taskModel BGemini 3.8 FlashGoogle61.6/1006 independent benchmarks$2.74 per solved task
Shared results
118
Claude Fable 5.1 only
6
Gemini 3.8 Flash only
10
Like-for-like categories
8 of 9

Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.

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 84.2 from 5 benchmarks, Gemini 3.8 Flash 61.6 from 6 benchmarks.
Widest category
Math, 24.1 points apart on average over 6 shared benchmarks.
Widest single gap
FrontierMath, tier 4: Claude Fable 5.1 87.8% against Gemini 3.8 Flash 22.0%, 65.9 points apart on a 0 to 100 scale.
Output price
Claude Fable 5.1 $50.00 against Gemini 3.8 Flash $3.75 per million output tokens, 13.3x apart.
Context window
Claude Fable 5.1 takes 1M tokens, Gemini 3.8 Flash 1.05M.

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 5.1BarsGemini 3.8 FlashTies
Coding240
Intelligence20
Agentic work201
Reasoning96
Math51
Knowledge100
Web design90
General256
All shared boards10414
CodingLike-for-likeSix of these boards feed the Vibe Coding Index240
Coding benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
LiveBench coding97.7%82.2%Claude Fable 5.1
LMArena WebDev17431585Claude Fable 5.1
AA Coding Index81.676.3Claude Fable 5.1
LiveCodeBench (Vals AI)90.5%89.5%Claude Fable 5.1
SWE-bench Verified (Vals AI)Not measured80.0%Only Gemini 3.8 Flash measured
Terminal-Bench 4 (Vals AI)58.1%19.7%Claude Fable 5.1
Vibe Code Bench (Vals AI)90.3%78.7%Claude Fable 5.1
Code migration (Vals AI)54.6%36.5%Claude Fable 5.1
ProgramBench (Vals AI)7.0%1.0%Claude Fable 5.1
IOI (Vals AI)90.8%56.9%Claude Fable 5.1
Terminal-Bench 2.1 (Vals AI)85.0%81.3%Claude Fable 5.1
SWE-bench Multimodal (Vals AI)61.3%40.8%Claude Fable 5.1
Vibe Code Bench 1-100 (Vals AI)28.0%18.8%Claude Fable 5.1
SkillsBench (Vals AI)61.5%58.0%Claude Fable 5.1
CyberBench (Vals AI)70.4%43.8%Claude Fable 5.1
SciCode63.1%56.6%Claude Fable 5.1
FrontierCode50.9%41.2%Claude Fable 5.1
FrontierSWE56.3%19.6%Claude Fable 5.1
GSO-Bench88.2%Not measuredOnly Claude Fable 5.1 measured
WeirdML92.9%84.8%Claude Fable 5.1
MirrorCode73.3%Not measuredOnly Claude Fable 5.1 measured
ALE-Bench2143.21269.7Claude Fable 5.1
LMArena Text: coding15321508Claude Fable 5.1
LMArena Text: software and IT15301507Claude Fable 5.1
LMArena WebDev: React17921577Claude Fable 5.1
LMArena WebDev: HTML16841616Claude Fable 5.1
LMArena WebDev: from an image17221593Claude Fable 5.1
SciCodeNot measured12.3%Only Gemini 3.8 Flash measured
Neither model has a result on the other 11 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index20
Intelligence benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
AA Intelligence Index53.440.9Claude Fable 5.1
Epoch Capabilities Index166.5157.4Claude Fable 5.1
Agentic workLike-for-likePublic boards, shown as published, kept out of the index201
Agentic work benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
AA Agentic Index57.940.2Claude Fable 5.1
Design Arena: agents building web apps13181238Claude Fable 5.1
Design Arena: agents building full-stack apps13261244Claude Fable 5.1
Design Arena: agents building mobile apps12671236Claude Fable 5.1
Design Arena: agents building Android appsNot measured1078Only Gemini 3.8 Flash measured
Design Arena: agents building Godot games13271273Claude Fable 5.1
Design Arena: PowerPoint slides13051153Claude Fable 5.1
Design Arena: spreadsheets13801022Claude Fable 5.1
LiveBench research82.0%79.1%Claude Fable 5.1
LiveBench browser100.0%64.0%Claude Fable 5.1
LiveBench long agentic80.8%30.1%Claude Fable 5.1
SREBench (Vals AI)22.9%11.1%Claude Fable 5.1
Finance Agent (Vals AI)58.9%61.4%Gemini 3.8 Flash
Tax Agent Bench (Vals AI)49.2%32.1%Claude Fable 5.1
Legal Research Bench (Vals AI)55.3%38.9%Claude Fable 5.1
Harvey's Legal Agent Benchmark (Vals AI)Not measured12.1%Only Gemini 3.8 Flash measured
Excel Modeling Benchmark (Vals AI)76.7%72.2%Claude Fable 5.1
BioMysteryBench (Vals AI)Not measured62.2%Only Gemini 3.8 Flash measured
Terminal-Bench-Science (Vals AI)40.0%8.6%Claude Fable 5.1
Vals Science IndexNot measured35.8%Only Gemini 3.8 Flash measured
Time Horizon Index (Vals AI)63.3%18.8%Claude Fable 5.1
CUA-bench (Vals AI)13.2%4.2%Claude Fable 5.1
Robo-bench (Vals AI)5.8%Not measuredOnly Claude Fable 5.1 measured
APEX-Agents68.6%64.3%Claude Fable 5.1
Remote Labor Index17.9%5.8%Claude Fable 5.1
SpireClimb2.0%Not measuredOnly Claude Fable 5.1 measured
Vending-Bench 2$5,422$5,094Claude Fable 5.1
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 index96
Reasoning benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
GPQA Diamond93.4%94.4%Gemini 3.8 Flash
LiveBench reasoning91.7%89.3%Claude Fable 5.1
MysteryMechanism (Vals AI)47.8%36.5%Claude Fable 5.1
MMMU Pro (Vals AI)90.6%89.1%Claude Fable 5.1
GPQA Diamond (Artificial Analysis run)93.7%95.3%Gemini 3.8 Flash
Humanity's Last Exam (Artificial Analysis run)59.1%47.8%Claude Fable 5.1
GPQA Diamond (Epoch AI run)Not measured95.4%Only Gemini 3.8 Flash measured
ARC-AGI97.5%98.5%Gemini 3.8 Flash
ARC-AGI-290.0%89.2%Claude Fable 5.1
Chess puzzles48.0%58.0%Gemini 3.8 Flash
Mystery game puzzles58.0%47.0%Claude Fable 5.1
EBR-bench57.1%Not measuredOnly Claude Fable 5.1 measured
LMArena Text: hard prompts15281509Claude Fable 5.1
LMArena Text: expert15441526Claude Fable 5.1
LMArena Text: hard prompts in English15221504Claude Fable 5.1
LMArena Vision: diagrams13431345Gemini 3.8 Flash
LMArena Vision: homework13451351Gemini 3.8 Flash
Neither model has a result on the other 5 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index51
Math benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
OTIS Mock AIME100.0%98.9%Claude Fable 5.1
FrontierMath, tiers 1 to 390.2%68.4%Claude Fable 5.1
FrontierMath, tier 487.8%22.0%Claude Fable 5.1
ProofBench100.0%48.0%Claude Fable 5.1
LMArena Text: math15311532Gemini 3.8 Flash
LMArena Text: mathematical work15411519Claude 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 index100
Knowledge benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
MMLU Pro92.4%90.2%Claude Fable 5.1
LegalBench (Vals AI)88.5%87.0%Claude Fable 5.1
TaxEval (Vals AI)76.0%74.5%Claude Fable 5.1
MortgageTax (Vals AI)70.8%65.3%Claude Fable 5.1
MedCode (Vals AI)53.5%48.1%Claude Fable 5.1
SimpleQA Verified70.8%69.7%Claude Fable 5.1
LMArena Text: science15321523Claude Fable 5.1
LMArena Text: medicine and healthcare15311508Claude Fable 5.1
LMArena Text: legal and government15141497Claude Fable 5.1
LMArena Text: business and finance14931479Claude Fable 5.1
FACTS Benchmark SuiteNot measured69.4%Only Gemini 3.8 Flash measured
Neither model has a result on the other 7 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index90
Web design benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
Design Arena: websites13121300Claude Fable 5.1
Design Arena: UI components13361316Claude Fable 5.1
Design Arena: game dev13811304Claude Fable 5.1
Design Arena: data viz13441270Claude Fable 5.1
Design Arena: 3D13921294Claude Fable 5.1
Design Arena: all code categories13351303Claude Fable 5.1
Design Arena: SVG13001296Claude Fable 5.1
Design Arena: ASCII art13231262Claude Fable 5.1
LiveBench design83.4%72.7%Claude Fable 5.1
GeneralLike-for-likePublic boards, shown as published, kept out of the index256
General benchmarks for Claude Fable 5.1 and Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
Vals IndexNot measured56.0%Only Gemini 3.8 Flash measured
LiveBench data analysis80.3%54.0%Claude Fable 5.1
Public Benefits Bench (Vals AI)74.9%65.3%Claude Fable 5.1
SAGE (Vals AI)48.5%35.1%Claude Fable 5.1
MedScribe (Vals AI)91.3%84.5%Claude Fable 5.1
Long context reasoning (AA-LCR)85.3%84.0%Claude Fable 5.1
DTBench97.6%95.7%Claude Fable 5.1
LMCA65.5%52.9%Claude Fable 5.1
Surface Evolver BenchNot measured76.9%Only Gemini 3.8 Flash measured
Furniture assembly70.0%31.7%Claude Fable 5.1
LMArena Text15121499Claude Fable 5.1
LMArena Text: instruction following15181492Claude Fable 5.1
LMArena Text: creative writing15091488Claude Fable 5.1
LMArena Vision13191315Claude Fable 5.1
LMArena Text: English15061498Claude Fable 5.1
LMArena Text: non-English15081491Claude Fable 5.1
LMArena Text: Chinese15841553Claude Fable 5.1
LMArena Text: German14991501Gemini 3.8 Flash
LMArena Text: Japanese15621507Claude Fable 5.1
LMArena Text: Korean15171464Claude Fable 5.1
LMArena Text: French15231496Claude Fable 5.1
LMArena Text: Spanish15201487Claude Fable 5.1
LMArena Text: Russian15201514Claude Fable 5.1
LMArena Text: Polish15251497Claude Fable 5.1
LMArena Text: multi-turn14931503Gemini 3.8 Flash
LMArena Text: longer queries15241507Claude Fable 5.1
LMArena Text: writing and language15101494Claude Fable 5.1
LMArena Text: entertainment and media14971480Claude Fable 5.1
LMArena Vision: English13131318Gemini 3.8 Flash
LMArena Vision: Chinese13911416Gemini 3.8 Flash
LMArena Vision: reading text13271333Gemini 3.8 Flash
LMArena Vision: humor13181321Gemini 3.8 Flash
LMArena Vision: creative writing13301299Claude Fable 5.1
Neither model has a result on the other 13 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 Gemini 3.8 Flash
BenchmarkClaude Fable 5.1Gemini 3.8 FlashLeader
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
Gemini 3.8 Flash$0.0026Fits in one request

Gemini 3.8 Flash costs less

Repository review

50K input + 3K output tokens

Claude Fable 5.1$0.650Fits in one request
Gemini 3.8 Flash$0.049Fits in one request

Gemini 3.8 Flash costs less

Agent loop

200K input + 10K output tokens

Claude Fable 5.1$2.50Fits in one request
Gemini 3.8 Flash$0.188Fits in one request

Gemini 3.8 Flash 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 Gemini 3.8 Flash
SpecificationAnthropic Claude Fable 5.1Google Gemini 3.8 Flash
MakerAnthropicGoogle
WeightsNo public weights listedNo public weights listed
ReleasedSeptember 1, 2026September 2, 2026
Context window1M1.05M
Input $/Mtok$10.00$0.75
Output $/Mtok$50.00$3.75
Coding index84.261.6
Independent measurements behind it56
Cost per solved taskNot computable$2.74
SourceOpenRouter listingOpenRouter listing

Questions

Is Claude Fable 5.1 better than Gemini 3.8 Flash for coding?

Pick Claude Fable 5.1 for coding: it scores 84.2 on the Vibe Coding Index against 61.6 for Gemini 3.8 Flash, though on 5 benchmarks against 6. Pick Gemini 3.8 Flash for output tokens 13.3x cheaper ($3.75 vs $50.00 per million) and a larger context window (1.05M against 1M tokens).

Which is cheaper, Claude Fable 5.1 or Gemini 3.8 Flash?

Claude Fable 5.1 costs $10.00 per million input tokens and $50.00 per million output tokens; Gemini 3.8 Flash costs $0.75 and $3.75. Cost per solved task is known for Gemini 3.8 Flash only.

Which has the bigger context window, Claude Fable 5.1 or Gemini 3.8 Flash?

Gemini 3.8 Flash, with 1.05M tokens against 1M.

How many benchmarks is the Claude Fable 5.1 vs Gemini 3.8 Flash comparison based on?

118 benchmarks have a result for both models as of October 22, 2026. Claude Fable 5.1's coding index rests on 5 independent benchmarks and Gemini 3.8 Flash's on 6. Where only one model has a result, the page says so instead of naming a winner.

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