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Gemini 3.5 Flash vs GPT-5.6 Luna

GPT-5.6 Luna leads Gemini 3.5 Flash on coding, 58.0 to 39.8 on the Vibe Coding Index, and GPT-5.6 Luna costs 7.5x less per output token ($1.20 vs $9.00 per million). Updated October 22, 2026; 99 benchmarks have a result for both.

Replace Gemini 3.5 Flash Replace GPT-5.6 Luna
Gemini 3.5 FlashGoogle
Coding
39.8
Overall
63.8
Output $/M
$9.00
70
GPT-5.6 LunaOpenAI
Coding
58.0
Overall
61.6
Output $/M
$1.20
28
vs boards won of 99 shared, 1 tied

Gemini 3.5 Flash or GPT-5.6 Luna: which to pick

Pick GPT-5.6 Luna for coding: it scores 58.0 on the Vibe Coding Index against 39.8 for Gemini 3.5 Flash.

Pick Gemini 3.5 Flash for work measured by SciCode or WeirdML, where it leads.

Model AGemini 3.5 FlashGoogle39.8/1004 independent benchmarks$1.21 per solved taskModel BGPT-5.6 LunaOpenAI58.0/1006 independent benchmarks$0.04 per solved task
Shared results
99
Gemini 3.5 Flash only
13
GPT-5.6 Luna only
20
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
Gemini 3.5 Flash 39.8 from 4 benchmarks, GPT-5.6 Luna 58.0 from 6 benchmarks.
Widest category
Math, 16.1 points apart on average over 6 shared benchmarks.
Widest single gap
FrontierMath, tier 4: Gemini 3.5 Flash 26.8% against GPT-5.6 Luna 61.0%, 34.1 points apart on a 0 to 100 scale.
Output price
Gemini 3.5 Flash $9.00 against GPT-5.6 Luna $1.20 per million output tokens, 7.5x apart.
Context window
Gemini 3.5 Flash takes 1.05M tokens, GPT-5.6 Luna 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
CategoryGemini 3.5 FlashBarsGPT-5.6 LunaTies
Coding6101 tie
Intelligence02
Agentic work34
Reasoning150
Math24
Knowledge102
Web design80
General266
All shared boards70281 tie
CodingLike-for-likeSix of these boards feed the Vibe Coding Index610
Coding benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
LiveBench codingNot measured73.6%Only GPT-5.6 Luna measured
LMArena WebDev14991518GPT-5.6 Luna
AA Coding IndexNot measured71.4Only GPT-5.6 Luna measured
LiveCodeBench (Vals AI)87.6%Not measuredOnly Gemini 3.5 Flash measured
SWE-bench Verified (Vals AI)78.8%93.0%GPT-5.6 Luna
Terminal-Bench 4 (Vals AI)6.1%11.6%GPT-5.6 Luna
Vibe Code Bench (Vals AI)48.7%77.1%GPT-5.6 Luna
Code migration (Vals AI)26.8%44.5%GPT-5.6 Luna
ProgramBench (Vals AI)0.0%0.0%Tie
IOI (Vals AI)Not measured61.8%Only GPT-5.6 Luna measured
Terminal-Bench 2.1 (Vals AI)74.2%79.0%GPT-5.6 Luna
Vibe Code Bench 1-100 (Vals AI)Not measured22.6%Only GPT-5.6 Luna measured
SkillsBench (Vals AI)52.7%60.5%GPT-5.6 Luna
CyberBench (Vals AI)Not measured73.6%Only GPT-5.6 Luna measured
SciCode53.9%53.6%Gemini 3.5 Flash
Terminal-Bench Hard (Artificial Analysis run)46.2%Not measuredOnly Gemini 3.5 Flash measured
FrontierCodeNot measured39.8%Only GPT-5.6 Luna measured
WeirdML62.6%60.9%Gemini 3.5 Flash
ALE-Bench911.01667.4GPT-5.6 Luna
LMArena Text: coding14931466Gemini 3.5 Flash
LMArena Text: software and IT14941463Gemini 3.5 Flash
LMArena WebDev: React14951508GPT-5.6 Luna
LMArena WebDev: HTML15221520Gemini 3.5 Flash
LMArena WebDev: from an image15041517GPT-5.6 Luna
SciCode12.3%6.2%Gemini 3.5 Flash
Neither model has a result on the other 14 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index02
Intelligence benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
AA Intelligence Index33.637.3GPT-5.6 Luna
Epoch Capabilities Index154.9156.5GPT-5.6 Luna
Agentic workLike-for-likePublic boards, shown as published, kept out of the index34
Agentic work benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
AA Agentic IndexNot measured42.1Only GPT-5.6 Luna measured
Design Arena: agents building web apps1202Not measuredOnly Gemini 3.5 Flash measured
Design Arena: agents building full-stack apps1197Not measuredOnly Gemini 3.5 Flash measured
Design Arena: agents building mobile apps1174Not measuredOnly Gemini 3.5 Flash measured
Design Arena: agents building Android apps1185Not measuredOnly Gemini 3.5 Flash measured
Design Arena: agents building Godot games1098Not measuredOnly Gemini 3.5 Flash measured
Design Arena: agents building games1180Not measuredOnly Gemini 3.5 Flash measured
Design Arena: HTML slides1093Not measuredOnly Gemini 3.5 Flash measured
Design Arena: PowerPoint slides1154Not measuredOnly Gemini 3.5 Flash measured
LiveBench researchNot measured51.0%Only GPT-5.6 Luna measured
LiveBench browserNot measured68.0%Only GPT-5.6 Luna measured
LiveBench long agenticNot measured30.4%Only GPT-5.6 Luna measured
SREBench (Vals AI)Not measured1.5%Only GPT-5.6 Luna measured
Finance Agent (Vals AI)57.9%55.0%Gemini 3.5 Flash
Tax Agent Bench (Vals AI)21.6%24.8%GPT-5.6 Luna
Legal Research Bench (Vals AI)30.8%36.5%GPT-5.6 Luna
Excel Modeling Benchmark (Vals AI)63.5%67.1%GPT-5.6 Luna
BioMysteryBench (Vals AI)Not measured61.5%Only GPT-5.6 Luna measured
Terminal-Bench-Science (Vals AI)5.7%0.0%Gemini 3.5 Flash
Vals Science IndexNot measured25.3%Only GPT-5.6 Luna measured
τ²-Bench Telecom95.6%Not measuredOnly Gemini 3.5 Flash measured
APEX-Agents27.5%43.0%GPT-5.6 Luna
BALROGNot measured45.6%Only GPT-5.6 Luna measured
Vending-Bench 2$5,396$4,095Gemini 3.5 Flash
Neither model has a result on the other 17 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index150
Reasoning benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
GPQA Diamond92.7%91.7%Gemini 3.5 Flash
LiveBench reasoningNot measured85.6%Only GPT-5.6 Luna measured
MysteryMechanism (Vals AI)Not measured14.4%Only GPT-5.6 Luna measured
MMMU Pro (Vals AI)88.3%85.0%Gemini 3.5 Flash
GPQA Diamond (Artificial Analysis run)92.2%91.1%Gemini 3.5 Flash
Humanity's Last Exam (Artificial Analysis run)42.7%39.5%Gemini 3.5 Flash
GPQA Diamond (Epoch AI run)92.8%91.6%Gemini 3.5 Flash
ARC-AGI92.5%88.0%Gemini 3.5 Flash
ARC-AGI-272.1%59.5%Gemini 3.5 Flash
SimpleBench76.7%46.8%Gemini 3.5 Flash
Chess puzzles45.0%43.0%Gemini 3.5 Flash
Mystery game puzzles32.0%21.0%Gemini 3.5 Flash
EBR-bench4.8%Not measuredOnly Gemini 3.5 Flash measured
LMArena Text: hard prompts14881451Gemini 3.5 Flash
LMArena Text: expert14951478Gemini 3.5 Flash
LMArena Text: hard prompts in English14831460Gemini 3.5 Flash
LMArena Vision: diagrams13231273Gemini 3.5 Flash
LMArena Vision: homework13301282Gemini 3.5 Flash
Kagi LLM BenchmarkNot measured49.1%Only GPT-5.6 Luna measured
Neither model has a result on the other 3 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index24
Math benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
OTIS Mock AIME95.6%98.3%GPT-5.6 Luna
FrontierMath, tiers 1 to 362.8%82.1%GPT-5.6 Luna
FrontierMath, tier 426.8%61.0%GPT-5.6 Luna
ProofBench31.0%60.0%GPT-5.6 Luna
LMArena Text: math15041459Gemini 3.5 Flash
LMArena Text: mathematical work14951470Gemini 3.5 Flash
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index102
Knowledge benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
MMLU Pro89.5%86.0%Gemini 3.5 Flash
LegalBench (Vals AI)83.6%84.0%GPT-5.6 Luna
CorpFin (Vals AI)64.7%64.2%Gemini 3.5 Flash
TaxEval (Vals AI)74.4%76.2%GPT-5.6 Luna
MortgageTax (Vals AI)68.1%67.3%Gemini 3.5 Flash
MedCode (Vals AI)55.8%42.4%Gemini 3.5 Flash
SimpleQA Verified66.2%41.0%Gemini 3.5 Flash
LMArena Text: science14951433Gemini 3.5 Flash
LMArena Text: medicine and healthcare14831399Gemini 3.5 Flash
LMArena Text: legal and government14881446Gemini 3.5 Flash
LMArena Text: business and finance14671439Gemini 3.5 Flash
FACTS Benchmark Suite63.1%35.0%Gemini 3.5 Flash
Neither model has a result on the other 6 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index80
Web design benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
Design Arena: websites12671255Gemini 3.5 Flash
Design Arena: UI components12691248Gemini 3.5 Flash
Design Arena: game dev12631194Gemini 3.5 Flash
Design Arena: data viz12361211Gemini 3.5 Flash
Design Arena: 3D12431121Gemini 3.5 Flash
Design Arena: all code categories12661231Gemini 3.5 Flash
Design Arena: SVG12531194Gemini 3.5 Flash
Design Arena: ASCII art12541142Gemini 3.5 Flash
LiveBench designNot measured76.0%Only GPT-5.6 Luna measured
GeneralLike-for-likePublic boards, shown as published, kept out of the index266
General benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
LiveBench data analysisNot measured78.0%Only GPT-5.6 Luna measured
Public Benefits Bench (Vals AI)59.5%61.2%GPT-5.6 Luna
SAGE (Vals AI)49.9%44.2%Gemini 3.5 Flash
MedScribe (Vals AI)76.6%84.4%GPT-5.6 Luna
Vals Multimodal Index62.9%69.1%GPT-5.6 Luna
IFBench76.3%Not measuredOnly Gemini 3.5 Flash measured
Long context reasoning (AA-LCR)74.3%83.7%GPT-5.6 Luna
DTBench94.7%89.1%Gemini 3.5 Flash
LMCA47.1%48.5%GPT-5.6 Luna
Surface Evolver Bench58.1%61.9%GPT-5.6 Luna
Furniture assemblyNot measured42.5%Only GPT-5.6 Luna measured
LMArena Text14821431Gemini 3.5 Flash
LMArena Text: instruction following14671437Gemini 3.5 Flash
LMArena Text: creative writing14701396Gemini 3.5 Flash
LMArena Vision13081257Gemini 3.5 Flash
LMArena Text: English14811441Gemini 3.5 Flash
LMArena Text: non-English14751417Gemini 3.5 Flash
LMArena Text: Chinese15271470Gemini 3.5 Flash
LMArena Text: German14941455Gemini 3.5 Flash
LMArena Text: Japanese14861415Gemini 3.5 Flash
LMArena Text: Korean14481415Gemini 3.5 Flash
LMArena Text: French14901458Gemini 3.5 Flash
LMArena Text: Spanish14801446Gemini 3.5 Flash
LMArena Text: Russian14931427Gemini 3.5 Flash
LMArena Text: Polish15161405Gemini 3.5 Flash
LMArena Text: multi-turn14811434Gemini 3.5 Flash
LMArena Text: longer queries14831436Gemini 3.5 Flash
LMArena Text: writing and language14781419Gemini 3.5 Flash
LMArena Text: entertainment and media14591402Gemini 3.5 Flash
LMArena Vision: English13051263Gemini 3.5 Flash
LMArena Vision: Chinese13771294Gemini 3.5 Flash
LMArena Vision: reading text13171264Gemini 3.5 Flash
LMArena Vision: humor13211190Gemini 3.5 Flash
LMArena Vision: creative writing13011257Gemini 3.5 Flash
LMArena Document14631457Gemini 3.5 Flash
Neither model has a result on the other 11 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for Gemini 3.5 Flash and GPT-5.6 Luna
BenchmarkGemini 3.5 FlashGPT-5.6 LunaLeader
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

Gemini 3.5 Flash$0.0060Fits in one request
GPT-5.6 Luna$0.0008Fits in one request

GPT-5.6 Luna costs less

Repository review

50K input + 3K output tokens

Gemini 3.5 Flash$0.102Fits in one request
GPT-5.6 Luna$0.014Fits in one request

GPT-5.6 Luna costs less

Agent loop

200K input + 10K output tokens

Gemini 3.5 Flash$0.390Fits in one request
GPT-5.6 Luna$0.052Fits in one request

GPT-5.6 Luna 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 Gemini 3.5 Flash and GPT-5.6 Luna
SpecificationGoogle Gemini 3.5 FlashOpenAI GPT-5.6 Luna
MakerGoogleOpenAI
WeightsNo public weights listedNo public weights listed
ReleasedMay 19, 2026July 9, 2026
Context window1.05M1.05M
Input $/Mtok$1.50$0.20
Output $/Mtok$9.00$1.20
Coding index39.858.0
Independent measurements behind it46
Cost per solved task$1.21$0.04
SourceOpenRouter listingOpenRouter listing

Questions

Is Gemini 3.5 Flash better than GPT-5.6 Luna for coding?

Pick GPT-5.6 Luna for coding: it scores 58.0 on the Vibe Coding Index against 39.8 for Gemini 3.5 Flash. Pick Gemini 3.5 Flash for work measured by SciCode or WeirdML, where it leads.

Which is cheaper, Gemini 3.5 Flash or GPT-5.6 Luna?

Gemini 3.5 Flash costs $1.50 per million input tokens and $9.00 per million output tokens; GPT-5.6 Luna costs $0.20 and $1.20. Per solved SWE-bench Verified task, Gemini 3.5 Flash costs $1.21 and GPT-5.6 Luna $0.04.

Which has the bigger context window, Gemini 3.5 Flash or GPT-5.6 Luna?

GPT-5.6 Luna, with 1.05M tokens against 1.05M.

How many benchmarks is the Gemini 3.5 Flash vs GPT-5.6 Luna comparison based on?

99 benchmarks have a result for both models as of October 22, 2026. Gemini 3.5 Flash's coding index rests on 4 independent benchmarks and GPT-5.6 Luna's on 6. Where only one model has a result, the page says so instead of naming a winner.

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