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Gemini 2.5 Flash vs GPT-5.6 Luna

Updated October 21, 2026. 58 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace Gemini 2.5 Flash Replace GPT-5.6 Luna
Gemini 2.5 FlashGoogle
Coding
28.7
Overall
15.5
Output $/M
$2.50
5
GPT-5.6 LunaOpenAI
Coding
61.5
Overall
37.3
Output $/M
$1.20
53
vs boards won of 58 shared

Decision reading

Pick GPT-5.6 Luna for coding: it scores 61.5 on the Vibe Coding Index against 28.7 for Gemini 2.5 Flash.

Pick Gemini 2.5 Flash when what matters is LMArena Text: medicine and healthcare or SAGE (Vals AI), where it leads.

Model AGemini 2.5 FlashGoogle28.7/1001 independent benchmark$0.466 per solved taskModel BGPT-5.6 LunaOpenAI61.5/1002 independent benchmarks$0.04 per solved task
Shared results
58
Gemini 2.5 Flash only
11
GPT-5.6 Luna only
58
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
Gemini 2.5 Flash 28.7 from 1 benchmark, GPT-5.6 Luna 61.5 from 2 benchmarks.
Widest category
Web design, 21.7 points apart on average over 7 shared benchmarks.
Widest single gap
ARC-AGI-2: Gemini 2.5 Flash 2.5% against GPT-5.6 Luna 59.5%, 57.0 points apart on a 0 to 100 scale.
Output price
Gemini 2.5 Flash $2.50 against GPT-5.6 Luna $1.20 per million output tokens, 2.1x apart.
Context window
Gemini 2.5 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 2.5 FlashBarsGPT-5.6 LunaTies
Coding02
Intelligence02
Agentic work02
Reasoning010
Math02
Knowledge14
Web design07
General424
All shared boards553
CodingLike-for-likeFour of these boards feed the Vibe Coding Index02
Coding benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
SWE-bench Verified28.7%Not measuredOnly Gemini 2.5 Flash measured
LiveBench codingNot measured73.6%Only GPT-5.6 Luna measured
LMArena WebDevNot measured1518Only GPT-5.6 Luna measured
AA Coding IndexNot measured71.4Only GPT-5.6 Luna measured
SWE-bench Verified (Vals AI)Not measured93.0%Only GPT-5.6 Luna measured
Terminal-Bench 4 (Vals AI)Not measured11.6%Only GPT-5.6 Luna measured
Vibe Code Bench (Vals AI)Not measured77.1%Only GPT-5.6 Luna measured
Code migration (Vals AI)Not measured44.5%Only GPT-5.6 Luna measured
ProgramBench (Vals AI)Not measured0.0%Only GPT-5.6 Luna measured
IOI (Vals AI)Not measured61.8%Only GPT-5.6 Luna measured
Terminal-Bench 2.1 (Vals AI)Not measured79.0%Only GPT-5.6 Luna measured
Vibe Code Bench 1-100 (Vals AI)Not measured22.6%Only GPT-5.6 Luna measured
SkillsBench (Vals AI)Not measured60.5%Only GPT-5.6 Luna measured
CyberBench (Vals AI)Not measured73.6%Only GPT-5.6 Luna measured
LiveCodeBench (Artificial Analysis run)69.5%Not measuredOnly Gemini 2.5 Flash measured
SciCodeNot measured53.6%Only GPT-5.6 Luna measured
Terminal-Bench Hard (Artificial Analysis run)13.6%Not measuredOnly Gemini 2.5 Flash measured
Terminal-Bench17.1%Not measuredOnly Gemini 2.5 Flash measured
FrontierCodeNot measured39.8%Only GPT-5.6 Luna measured
WeirdMLNot measured60.9%Only GPT-5.6 Luna measured
ALE-BenchNot measured1667.4Only GPT-5.6 Luna measured
LMArena Text: coding14231466GPT-5.6 Luna
LMArena Text: software and IT14251463GPT-5.6 Luna
LMArena WebDev: ReactNot measured1508Only GPT-5.6 Luna measured
LMArena WebDev: HTMLNot measured1520Only GPT-5.6 Luna measured
LMArena WebDev: from an imageNot measured1517Only GPT-5.6 Luna measured
Neither model has a result on the other 12 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index02
Intelligence benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
AA Intelligence Index15.537.3GPT-5.6 Luna
Epoch Capabilities Index142.9156.5GPT-5.6 Luna
Agentic workLike-for-likePublic boards, shown as published, kept out of the index02
Agentic work benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
AA Agentic IndexNot measured42.1Only GPT-5.6 Luna 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)Not measured55.0%Only GPT-5.6 Luna measured
Tax Agent Bench (Vals AI)Not measured24.8%Only GPT-5.6 Luna measured
Legal Research Bench (Vals AI)Not measured36.5%Only GPT-5.6 Luna measured
Excel Modeling Benchmark (Vals AI)Not measured67.1%Only GPT-5.6 Luna measured
BioMysteryBench (Vals AI)Not measured61.5%Only GPT-5.6 Luna measured
Terminal-Bench-Science (Vals AI)Not measured0.0%Only GPT-5.6 Luna measured
Vals Science IndexNot measured25.3%Only GPT-5.6 Luna measured
τ²-Bench Telecom31.6%Not measuredOnly Gemini 2.5 Flash measured
APEX-AgentsNot measured43.0%Only GPT-5.6 Luna measured
BALROG33.5%45.6%GPT-5.6 Luna
Vending-Bench 2$549$4,095GPT-5.6 Luna
Neither model has a result on the other 23 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index010
Reasoning benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
GPQA DiamondNot measured91.7%Only GPT-5.6 Luna measured
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)Not measured85.0%Only GPT-5.6 Luna measured
GPQA Diamond (Artificial Analysis run)79.0%91.1%GPT-5.6 Luna
Humanity's Last Exam (Artificial Analysis run)12.1%39.5%GPT-5.6 Luna
GPQA Diamond (Epoch AI run)Not measured91.6%Only GPT-5.6 Luna measured
ARC-AGI33.3%88.0%GPT-5.6 Luna
ARC-AGI-22.5%59.5%GPT-5.6 Luna
SimpleBench41.2%46.8%GPT-5.6 Luna
Chess puzzlesNot measured43.0%Only GPT-5.6 Luna measured
Mystery game puzzlesNot measured21.0%Only GPT-5.6 Luna measured
LMArena Text: hard prompts14221451GPT-5.6 Luna
LMArena Text: expert14261478GPT-5.6 Luna
LMArena Text: hard prompts in English14201460GPT-5.6 Luna
LMArena Vision: diagrams12451273GPT-5.6 Luna
LMArena Vision: homework12441282GPT-5.6 Luna
Neither model has a result on the other 4 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index02
Math benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
AA Math Index73.3Not measuredOnly Gemini 2.5 Flash measured
AIME 2025 (Artificial Analysis run)73.3%Not measuredOnly Gemini 2.5 Flash measured
OTIS Mock AIMENot measured98.3%Only GPT-5.6 Luna measured
FrontierMath, tiers 1 to 3Not measured82.1%Only GPT-5.6 Luna measured
FrontierMath, tier 4Not measured61.0%Only GPT-5.6 Luna measured
ProofBenchNot measured60.0%Only GPT-5.6 Luna measured
LMArena Text: math14111459GPT-5.6 Luna
LMArena Text: mathematical work14221470GPT-5.6 Luna
Neither model has a result on the other 5 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index14
Knowledge benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
MMLU ProNot measured86.0%Only GPT-5.6 Luna measured
LegalBench (Vals AI)Not measured84.0%Only GPT-5.6 Luna measured
CorpFin (Vals AI)Not measured64.2%Only GPT-5.6 Luna measured
TaxEval (Vals AI)Not measured76.2%Only GPT-5.6 Luna measured
MortgageTax (Vals AI)Not measured67.3%Only GPT-5.6 Luna measured
MedCode (Vals AI)40.4%42.4%GPT-5.6 Luna
MMLU Pro (Artificial Analysis run)83.2%Not measuredOnly Gemini 2.5 Flash measured
SimpleQA VerifiedNot measured41.0%Only GPT-5.6 Luna measured
LMArena Text: science14331433GPT-5.6 Luna
LMArena Text: medicine and healthcare14281399Gemini 2.5 Flash
LMArena Text: legal and government14301446GPT-5.6 Luna
LMArena Text: business and finance14041439GPT-5.6 Luna
Neither model has a result on the other 5 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index07
Web design benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
Design Arena: websites10741256GPT-5.6 Luna
Design Arena: UI components10051250GPT-5.6 Luna
Design Arena: game dev10051196GPT-5.6 Luna
Design Arena: data viz10601212GPT-5.6 Luna
Design Arena: 3D10211121GPT-5.6 Luna
Design Arena: all code categories10591231GPT-5.6 Luna
Design Arena: SVG10181193GPT-5.6 Luna
Design Arena: ASCII artNot measured1144Only GPT-5.6 Luna measured
LiveBench designNot measured76.0%Only GPT-5.6 Luna measured
GeneralLike-for-likePublic boards, shown as published, kept out of the index424
General benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 FlashGPT-5.6 LunaLeader
LiveBench data analysisNot measured78.0%Only GPT-5.6 Luna measured
Public Benefits Bench (Vals AI)Not measured61.2%Only GPT-5.6 Luna measured
SAGE (Vals AI)44.8%44.2%Gemini 2.5 Flash
MedScribe (Vals AI)83.0%84.4%GPT-5.6 Luna
Vals Multimodal IndexNot measured69.1%Only GPT-5.6 Luna measured
IFBench50.3%Not measuredOnly Gemini 2.5 Flash measured
Long context reasoning (AA-LCR)65.3%83.7%GPT-5.6 Luna
DTBench76.5%89.1%GPT-5.6 Luna
LMCA27.5%48.5%GPT-5.6 Luna
Surface Evolver BenchNot measured61.9%Only GPT-5.6 Luna measured
Furniture assemblyNot measured42.5%Only GPT-5.6 Luna measured
LMArena Text14171431GPT-5.6 Luna
LMArena Text: instruction following14051437GPT-5.6 Luna
LMArena Text: creative writing14001396Gemini 2.5 Flash
LMArena Vision12351257GPT-5.6 Luna
LMArena Text: English14181441GPT-5.6 Luna
LMArena Text: non-English14091417GPT-5.6 Luna
LMArena Text: Chinese14491470GPT-5.6 Luna
LMArena Text: German14171455GPT-5.6 Luna
LMArena Text: Japanese13961415GPT-5.6 Luna
LMArena Text: Korean13851415GPT-5.6 Luna
LMArena Text: French14321458GPT-5.6 Luna
LMArena Text: Spanish14221446GPT-5.6 Luna
LMArena Text: Russian14151427GPT-5.6 Luna
LMArena Text: Polish14131405Gemini 2.5 Flash
LMArena Text: multi-turn14081434GPT-5.6 Luna
LMArena Text: longer queries14191436GPT-5.6 Luna
LMArena Text: writing and language14051419GPT-5.6 Luna
LMArena Text: entertainment and media13931402GPT-5.6 Luna
LMArena Vision: English12391263GPT-5.6 Luna
LMArena Vision: Chinese12841294GPT-5.6 Luna
LMArena Vision: reading text12371264GPT-5.6 Luna
LMArena Vision: humor12251190Gemini 2.5 Flash
LMArena Vision: captioning1277Not measuredOnly Gemini 2.5 Flash measured
LMArena Vision: recognizing things1252Not measuredOnly Gemini 2.5 Flash measured
LMArena Vision: creative writing12411257GPT-5.6 Luna
LMArena DocumentNot measured1457Only GPT-5.6 Luna measured
Neither model has a result on the other 9 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for Gemini 2.5 Flash and GPT-5.6 Luna
BenchmarkGemini 2.5 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 2.5 Flash$0.0015Fits 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 2.5 Flash$0.022Fits 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 2.5 Flash$0.085Fits 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 2.5 Flash and GPT-5.6 Luna
SpecificationGoogle Gemini 2.5 FlashOpenAI GPT-5.6 Luna
MakerGoogleOpenAI
WeightsNo public weights listedNo public weights listed
ReleasedJune 17, 2025July 9, 2026
Context window1.05M1.05M
Input $/Mtok$0.30$0.20
Output $/Mtok$2.50$1.20
Coding index28.761.5
Independent measurements behind it12
Cost per solved task$0.466$0.04
SourceOpenRouter listingOpenRouter listing

Questions

Is Gemini 2.5 Flash better than GPT-5.6 Luna for coding?

Pick GPT-5.6 Luna for coding: it scores 61.5 on the Vibe Coding Index against 28.7 for Gemini 2.5 Flash. Pick Gemini 2.5 Flash when what matters is LMArena Text: medicine and healthcare or SAGE (Vals AI), where it leads.

Which is cheaper, Gemini 2.5 Flash or GPT-5.6 Luna?

Gemini 2.5 Flash costs $0.30 per million input tokens and $2.50 per million output tokens; GPT-5.6 Luna costs $0.20 and $1.20. Per solved SWE-bench Verified task, Gemini 2.5 Flash costs $0.466 and GPT-5.6 Luna $0.04.

Which has the bigger context window, Gemini 2.5 Flash or GPT-5.6 Luna?

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

How many benchmarks is the Gemini 2.5 Flash vs GPT-5.6 Luna comparison based on?

58 benchmarks have a result for both models as of October 21, 2026. Gemini 2.5 Flash's coding index rests on 1 independent benchmark and GPT-5.6 Luna's on 2. Where only one model has a result, the page says so instead of naming a winner.

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