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Claude Sonnet 5.5 vs Gemini 3.8 Flash

Updated October 21, 2026. 94 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace Claude Sonnet 5.5 Replace Gemini 3.8 Flash
Claude Sonnet 5.5Anthropic
Coding
88.9
Overall
56.0
Output $/M
$10.00
64
Gemini 3.8 FlashGoogle
Coding
70.5
Overall
40.9
Output $/M
$4.125
30
vs boards won of 94 shared

Decision reading

Pick Claude Sonnet 5.5 for coding: it scores 88.9 on the Vibe Coding Index against 70.5 for Gemini 3.8 Flash.

Pick Gemini 3.8 Flash when output tokens cost 2.4x less, or when the context window is larger, 1.05M against 1M tokens.

Model AClaude Sonnet 5.5Anthropic88.9/1002 independent benchmarksNo cost per solved taskModel BGemini 3.8 FlashGoogle70.5/1002 independent benchmarks$2.74 per solved task
Shared results
94
Claude Sonnet 5.5 only
1
Gemini 3.8 Flash only
32
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 Sonnet 5.5 88.9 from 2 benchmarks, Gemini 3.8 Flash 70.5 from 2 benchmarks.
Widest category
Math, 23.2 points apart on average over 6 shared benchmarks.
Widest single gap
FrontierMath, tier 4: Claude Sonnet 5.5 80.5% against Gemini 3.8 Flash 22.0%, 58.5 points apart on a 0 to 100 scale.
Output price
Claude Sonnet 5.5 $10.00 against Gemini 3.8 Flash $4.125 per million output tokens, 2.4x apart.
Context window
Claude Sonnet 5.5 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 Sonnet 5.5BarsGemini 3.8 FlashTies
Coding181
Intelligence20
Agentic work152
Reasoning74
Math42
Knowledge15
Web design70
General1016
All shared boards6430
CodingLike-for-likeFour of these boards feed the Vibe Coding Index181
Coding benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
LiveBench coding94.7%82.2%Claude Sonnet 5.5
LMArena WebDev17681585Claude Sonnet 5.5
AA Coding IndexNot measured76.3Only Gemini 3.8 Flash measured
LiveCodeBench (Vals AI)Not measured89.5%Only Gemini 3.8 Flash measured
SWE-bench Verified (Vals AI)Not measured80.0%Only Gemini 3.8 Flash measured
Terminal-Bench 4 (Vals AI)64.1%19.7%Claude Sonnet 5.5
Vibe Code Bench (Vals AI)92.4%78.7%Claude Sonnet 5.5
Code migration (Vals AI)69.8%36.5%Claude Sonnet 5.5
ProgramBench (Vals AI)6.5%1.0%Claude Sonnet 5.5
IOI (Vals AI)83.1%56.9%Claude Sonnet 5.5
Terminal-Bench 2.1 (Vals AI)83.2%81.3%Claude Sonnet 5.5
SWE-bench Multimodal (Vals AI)58.3%40.8%Claude Sonnet 5.5
Vibe Code Bench 1-100 (Vals AI)Not measured18.8%Only Gemini 3.8 Flash measured
SkillsBench (Vals AI)Not measured58.0%Only Gemini 3.8 Flash measured
CyberBench (Vals AI)59.6%43.8%Claude Sonnet 5.5
SciCode61.0%56.6%Claude Sonnet 5.5
FrontierCode52.1%41.2%Claude Sonnet 5.5
FrontierSWE61.9%19.6%Claude Sonnet 5.5
WeirdMLNot measured84.8%Only Gemini 3.8 Flash measured
ALE-Bench1819.11269.7Claude Sonnet 5.5
LMArena Text: coding15131508Claude Sonnet 5.5
LMArena Text: software and IT15041507Gemini 3.8 Flash
LMArena WebDev: React18171577Claude Sonnet 5.5
LMArena WebDev: HTML17411616Claude Sonnet 5.5
LMArena WebDev: from an image17371593Claude Sonnet 5.5
Neither model has a result on the other 13 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index20
Intelligence benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
AA Intelligence Index56.040.9Claude Sonnet 5.5
Epoch Capabilities Index166.2157.4Claude Sonnet 5.5
Agentic workLike-for-likePublic boards, shown as published, kept out of the index152
Agentic work benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
AA Agentic IndexNot measured40.2Only Gemini 3.8 Flash measured
Design Arena: agents building web apps13031238Claude Sonnet 5.5
Design Arena: agents building full-stack appsNot measured1244Only Gemini 3.8 Flash measured
Design Arena: agents building mobile apps12651236Claude Sonnet 5.5
Design Arena: agents building Android appsNot measured1078Only Gemini 3.8 Flash measured
Design Arena: agents building Godot gamesNot measured1273Only Gemini 3.8 Flash measured
Design Arena: PowerPoint slidesNot measured1178Only Gemini 3.8 Flash measured
Design Arena: spreadsheets12451052Claude Sonnet 5.5
LiveBench research83.6%79.1%Claude Sonnet 5.5
LiveBench browser84.0%64.0%Claude Sonnet 5.5
LiveBench long agentic78.8%30.1%Claude Sonnet 5.5
SREBench (Vals AI)30.1%11.1%Claude Sonnet 5.5
Finance Agent (Vals AI)58.1%61.4%Gemini 3.8 Flash
Tax Agent Bench (Vals AI)42.0%32.1%Claude Sonnet 5.5
Legal Research Bench (Vals AI)48.1%38.9%Claude Sonnet 5.5
Harvey's Legal Agent Benchmark (Vals AI)10.4%12.1%Gemini 3.8 Flash
Excel Modeling Benchmark (Vals AI)75.7%72.2%Claude Sonnet 5.5
BioMysteryBench (Vals AI)81.1%62.2%Claude Sonnet 5.5
Terminal-Bench-Science (Vals AI)47.1%8.6%Claude Sonnet 5.5
Vals Science Index59.1%35.8%Claude Sonnet 5.5
Time Horizon Index (Vals AI)Not measured18.8%Only Gemini 3.8 Flash measured
CUA-bench (Vals AI)Not measured4.2%Only Gemini 3.8 Flash measured
APEX-Agents75.5%64.3%Claude Sonnet 5.5
Remote Labor IndexNot measured5.8%Only Gemini 3.8 Flash measured
SpireClimb1.3%Not measuredOnly Claude Sonnet 5.5 measured
Vending-Bench 2$11,165$5,094Claude Sonnet 5.5
Neither model has a result on the other 13 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index74
Reasoning benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
GPQA DiamondNot measured94.4%Only Gemini 3.8 Flash measured
LiveBench reasoning91.6%89.3%Claude Sonnet 5.5
MysteryMechanism (Vals AI)49.1%36.5%Claude Sonnet 5.5
MMMU Pro (Vals AI)Not measured89.1%Only Gemini 3.8 Flash measured
GPQA Diamond (Artificial Analysis run)Not measured95.3%Only Gemini 3.8 Flash measured
Humanity's Last Exam (Artificial Analysis run)55.0%47.8%Claude Sonnet 5.5
GPQA Diamond (Epoch AI run)95.6%95.4%Claude Sonnet 5.5
ARC-AGINot measured98.5%Only Gemini 3.8 Flash measured
ARC-AGI-2Not measured89.2%Only Gemini 3.8 Flash measured
Chess puzzles59.0%58.0%Claude Sonnet 5.5
Mystery game puzzles65.0%47.0%Claude Sonnet 5.5
LMArena Text: hard prompts14941509Gemini 3.8 Flash
LMArena Text: expert15311526Claude Sonnet 5.5
LMArena Text: hard prompts in English15021504Gemini 3.8 Flash
LMArena Vision: diagrams13291345Gemini 3.8 Flash
LMArena Vision: homework13311351Gemini 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 index42
Math benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
OTIS Mock AIME100.0%98.9%Claude Sonnet 5.5
FrontierMath, tiers 1 to 388.8%68.4%Claude Sonnet 5.5
FrontierMath, tier 480.5%22.0%Claude Sonnet 5.5
ProofBench100.0%48.0%Claude Sonnet 5.5
LMArena Text: math14971532Gemini 3.8 Flash
LMArena Text: mathematical work15101519Gemini 3.8 Flash
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index15
Knowledge benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
MMLU ProNot measured90.2%Only Gemini 3.8 Flash measured
LegalBench (Vals AI)Not measured87.0%Only Gemini 3.8 Flash measured
TaxEval (Vals AI)Not measured74.5%Only Gemini 3.8 Flash measured
MortgageTax (Vals AI)Not measured65.3%Only Gemini 3.8 Flash measured
MedCode (Vals AI)52.9%48.1%Claude Sonnet 5.5
SimpleQA Verified46.5%69.7%Gemini 3.8 Flash
LMArena Text: science14831523Gemini 3.8 Flash
LMArena Text: medicine and healthcare14641508Gemini 3.8 Flash
LMArena Text: legal and government14831497Gemini 3.8 Flash
LMArena Text: business and finance14681479Gemini 3.8 Flash
Neither model has a result on the other 7 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index70
Web design benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
Design Arena: websites13261301Claude Sonnet 5.5
Design Arena: UI components13671318Claude Sonnet 5.5
Design Arena: game dev14691305Claude Sonnet 5.5
Design Arena: data viz13891269Claude Sonnet 5.5
Design Arena: 3D14581295Claude Sonnet 5.5
Design Arena: all code categories13641304Claude Sonnet 5.5
Design Arena: SVGNot measured1295Only Gemini 3.8 Flash measured
Design Arena: ASCII artNot measured1264Only Gemini 3.8 Flash measured
LiveBench design85.0%72.7%Claude Sonnet 5.5
GeneralLike-for-likePublic boards, shown as published, kept out of the index1016
General benchmarks for Claude Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 3.8 FlashLeader
Vals Index70.8%56.0%Claude Sonnet 5.5
LiveBench data analysis59.5%54.0%Claude Sonnet 5.5
Public Benefits Bench (Vals AI)67.2%65.3%Claude Sonnet 5.5
SAGE (Vals AI)51.8%35.1%Claude Sonnet 5.5
MedScribe (Vals AI)91.1%84.5%Claude Sonnet 5.5
Long context reasoning (AA-LCR)82.7%84.0%Gemini 3.8 Flash
DTBench97.3%95.7%Claude Sonnet 5.5
LMCA68.3%52.9%Claude Sonnet 5.5
Surface Evolver BenchNot measured76.9%Only Gemini 3.8 Flash measured
Furniture assembly75.0%31.7%Claude Sonnet 5.5
LMArena Text14731499Gemini 3.8 Flash
LMArena Text: instruction following14921492Claude Sonnet 5.5
LMArena Text: creative writing14671488Gemini 3.8 Flash
LMArena Vision12871315Gemini 3.8 Flash
LMArena Text: English14841498Gemini 3.8 Flash
LMArena Text: non-English14561491Gemini 3.8 Flash
LMArena Text: Chinese15351553Gemini 3.8 Flash
LMArena Text: GermanNot measured1501Only Gemini 3.8 Flash measured
LMArena Text: JapaneseNot measured1507Only Gemini 3.8 Flash measured
LMArena Text: KoreanNot measured1464Only Gemini 3.8 Flash measured
LMArena Text: French14991496Claude Sonnet 5.5
LMArena Text: Spanish14511487Gemini 3.8 Flash
LMArena Text: Russian14541514Gemini 3.8 Flash
LMArena Text: PolishNot measured1497Only Gemini 3.8 Flash measured
LMArena Text: multi-turn14651503Gemini 3.8 Flash
LMArena Text: longer queries14951507Gemini 3.8 Flash
LMArena Text: writing and language14741494Gemini 3.8 Flash
LMArena Text: entertainment and media14611480Gemini 3.8 Flash
LMArena Vision: English12891318Gemini 3.8 Flash
LMArena Vision: ChineseNot measured1416Only Gemini 3.8 Flash measured
LMArena Vision: reading text12971333Gemini 3.8 Flash
LMArena Vision: humorNot measured1321Only Gemini 3.8 Flash measured
LMArena Vision: creative writing12421299Gemini 3.8 Flash
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 Sonnet 5.5 and Gemini 3.8 Flash
BenchmarkClaude Sonnet 5.5Gemini 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 Sonnet 5.5$0.0070Fits in one request
Gemini 3.8 Flash$0.0029Fits in one request

Gemini 3.8 Flash costs less

Repository review

50K input + 3K output tokens

Claude Sonnet 5.5$0.130Fits in one request
Gemini 3.8 Flash$0.054Fits in one request

Gemini 3.8 Flash costs less

Agent loop

200K input + 10K output tokens

Claude Sonnet 5.5$0.500Fits in one request
Gemini 3.8 Flash$0.206Fits 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 Sonnet 5.5 and Gemini 3.8 Flash
SpecificationAnthropic Claude Sonnet 5.5Google Gemini 3.8 Flash
MakerAnthropicGoogle
WeightsNo public weights listedNo public weights listed
ReleasedSeptember 28, 2026September 2, 2026
Context window1M1.05M
Input $/Mtok$2.00$0.825
Output $/Mtok$10.00$4.125
Coding index88.970.5
Independent measurements behind it22
Cost per solved taskNot computable$2.74
SourceOpenRouter listingOpenRouter listing

Questions

Is Claude Sonnet 5.5 better than Gemini 3.8 Flash for coding?

Pick Claude Sonnet 5.5 for coding: it scores 88.9 on the Vibe Coding Index against 70.5 for Gemini 3.8 Flash. Pick Gemini 3.8 Flash when output tokens cost 2.4x less, or when the context window is larger, 1.05M against 1M tokens.

Which is cheaper, Claude Sonnet 5.5 or Gemini 3.8 Flash?

Claude Sonnet 5.5 costs $2.00 per million input tokens and $10.00 per million output tokens; Gemini 3.8 Flash costs $0.825 and $4.125. Cost per solved task is known for Gemini 3.8 Flash only.

Which has the bigger context window, Claude Sonnet 5.5 or Gemini 3.8 Flash?

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

How many benchmarks is the Claude Sonnet 5.5 vs Gemini 3.8 Flash comparison based on?

94 benchmarks have a result for both models as of October 21, 2026. Claude Sonnet 5.5's coding index rests on 2 independent benchmarks and Gemini 3.8 Flash's on 2. Where only one model has a result, the page says so instead of naming a winner.

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