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GPT-5.6 Luna vs GPT-6 Astra

Updated October 21, 2026. 101 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace GPT-5.6 Luna Replace GPT-6 Astra
GPT-5.6 LunaOpenAI
Coding
61.5
Overall
37.3
Output $/M
$1.20
7
GPT-6 AstraOpenAI
Coding
88.7
Overall
52.7
Output $/M
$50.00
94
vs boards won of 101 shared

Decision reading

Pick GPT-6 Astra for coding: it scores 88.7 on the Vibe Coding Index against 61.5 for GPT-5.6 Luna.

Pick GPT-5.6 Luna when output tokens cost 41.7x less, or when what matters is CyberBench (Vals AI) or Finance Agent (Vals AI), where it leads.

Model AGPT-5.6 LunaOpenAI61.5/1002 independent benchmarks$0.04 per solved taskModel BGPT-6 AstraOpenAI88.7/1002 independent benchmarksNo cost per solved task
Shared results
101
GPT-5.6 Luna only
15
GPT-6 Astra only
18
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
GPT-5.6 Luna 61.5 from 2 benchmarks, GPT-6 Astra 88.7 from 2 benchmarks.
Widest category
Agentic work, 27.7 points apart on average over 15 shared benchmarks.
Widest single gap
Vending-Bench 2: GPT-5.6 Luna $4,095 against GPT-6 Astra $15,515, 71.4 points apart on a 0 to 100 scale.
Output price
GPT-5.6 Luna $1.20 against GPT-6 Astra $50.00 per million output tokens, 41.7x apart.
Context window
Both take 1.05M 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
CategoryGPT-5.6 LunaBarsGPT-6 AstraTies
Coding119
Intelligence02
Agentic work213
Reasoning014
Math06
Knowledge06
Web design09
General425
All shared boards794
CodingLike-for-likeFour of these boards feed the Vibe Coding Index119
Coding benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
LiveBench coding73.6%93.7%GPT-6 Astra
LMArena WebDev15181774GPT-6 Astra
AA Coding Index71.476.9GPT-6 Astra
SWE-bench Verified (Vals AI)93.0%Not measuredOnly GPT-5.6 Luna measured
Terminal-Bench 4 (Vals AI)11.6%59.6%GPT-6 Astra
Vibe Code Bench (Vals AI)77.1%89.6%GPT-6 Astra
Code migration (Vals AI)44.5%67.7%GPT-6 Astra
ProgramBench (Vals AI)0.0%5.5%GPT-6 Astra
IOI (Vals AI)61.8%100.0%GPT-6 Astra
Terminal-Bench 2.1 (Vals AI)79.0%87.3%GPT-6 Astra
SWE-bench Multimodal (Vals AI)Not measured43.3%Only GPT-6 Astra measured
Vibe Code Bench 1-100 (Vals AI)22.6%27.6%GPT-6 Astra
SkillsBench (Vals AI)60.5%Not measuredOnly GPT-5.6 Luna measured
CyberBench (Vals AI)73.6%41.1%GPT-5.6 Luna
SciCode53.6%56.5%GPT-6 Astra
FrontierCode39.8%53.3%GPT-6 Astra
FrontierSWENot measured65.5%Only GPT-6 Astra measured
GSO-BenchNot measured79.4%Only GPT-6 Astra measured
WeirdML60.9%93.3%GPT-6 Astra
MirrorCodeNot measured46.7%Only GPT-6 Astra measured
ALE-Bench1667.42951.3GPT-6 Astra
LMArena Text: coding14661489GPT-6 Astra
LMArena Text: software and IT14631474GPT-6 Astra
LMArena WebDev: React15081798GPT-6 Astra
LMArena WebDev: HTML15201775GPT-6 Astra
LMArena WebDev: from an image15171726GPT-6 Astra
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 GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
AA Intelligence Index37.352.7GPT-6 Astra
Epoch Capabilities Index156.5168.8GPT-6 Astra
Agentic workLike-for-likePublic boards, shown as published, kept out of the index213
Agentic work benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
AA Agentic Index42.151.0GPT-6 Astra
Design Arena: agents building web appsNot measured1372Only GPT-6 Astra measured
Design Arena: agents building full-stack appsNot measured1357Only GPT-6 Astra measured
Design Arena: agents building mobile appsNot measured1312Only GPT-6 Astra measured
Design Arena: agents building Godot gamesNot measured1348Only GPT-6 Astra measured
Design Arena: PowerPoint slidesNot measured1245Only GPT-6 Astra measured
Design Arena: spreadsheetsNot measured1380Only GPT-6 Astra measured
LiveBench research51.0%85.2%GPT-6 Astra
LiveBench browser68.0%84.0%GPT-6 Astra
LiveBench long agentic30.4%82.4%GPT-6 Astra
SREBench (Vals AI)1.5%56.9%GPT-6 Astra
Finance Agent (Vals AI)55.0%53.5%GPT-5.6 Luna
Tax Agent Bench (Vals AI)24.8%20.7%GPT-5.6 Luna
Legal Research Bench (Vals AI)36.5%39.4%GPT-6 Astra
Harvey's Legal Agent Benchmark (Vals AI)Not measured7.1%Only GPT-6 Astra measured
Excel Modeling Benchmark (Vals AI)67.1%71.7%GPT-6 Astra
BioMysteryBench (Vals AI)61.5%79.3%GPT-6 Astra
Terminal-Bench-Science (Vals AI)0.0%62.9%GPT-6 Astra
Vals Science Index25.3%65.1%GPT-6 Astra
Time Horizon Index (Vals AI)Not measured90.5%Only GPT-6 Astra measured
CUA-bench (Vals AI)Not measured19.2%Only GPT-6 Astra measured
Robo-bench (Vals AI)Not measured23.3%Only GPT-6 Astra measured
APEX-Agents43.0%64.7%GPT-6 Astra
Remote Labor IndexNot measured20.8%Only GPT-6 Astra measured
BALROG45.6%68.3%GPT-6 Astra
SpireClimbNot measured25.7%Only GPT-6 Astra measured
Vending-Bench 2$4,095$15,515GPT-6 Astra
Neither model has a result on the other 12 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index014
Reasoning benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
GPQA Diamond91.7%Not measuredOnly GPT-5.6 Luna measured
LiveBench reasoning85.6%92.7%GPT-6 Astra
MysteryMechanism (Vals AI)14.4%53.1%GPT-6 Astra
MMMU Pro (Vals AI)85.0%Not measuredOnly GPT-5.6 Luna measured
GPQA Diamond (Artificial Analysis run)91.1%96.3%GPT-6 Astra
Humanity's Last Exam (Artificial Analysis run)39.5%54.7%GPT-6 Astra
GPQA Diamond (Epoch AI run)91.6%95.8%GPT-6 Astra
ARC-AGI88.0%98.5%GPT-6 Astra
ARC-AGI-259.5%95.0%GPT-6 Astra
SimpleBench46.8%Not measuredOnly GPT-5.6 Luna measured
Chess puzzles43.0%74.0%GPT-6 Astra
Mystery game puzzles21.0%84.0%GPT-6 Astra
EBR-benchNot measured76.2%Only GPT-6 Astra measured
LMArena Text: hard prompts14511463GPT-6 Astra
LMArena Text: expert14781489GPT-6 Astra
LMArena Text: hard prompts in English14601464GPT-6 Astra
LMArena Vision: diagrams12731297GPT-6 Astra
LMArena Vision: homework12821337GPT-6 Astra
Neither model has a result on the other 3 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index06
Math benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
OTIS Mock AIME98.3%100.0%GPT-6 Astra
FrontierMath, tiers 1 to 382.1%93.7%GPT-6 Astra
FrontierMath, tier 461.0%97.6%GPT-6 Astra
ProofBench60.0%99.0%GPT-6 Astra
LMArena Text: math14591465GPT-6 Astra
LMArena Text: mathematical work14701484GPT-6 Astra
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index06
Knowledge benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
MMLU Pro86.0%Not measuredOnly GPT-5.6 Luna measured
LegalBench (Vals AI)84.0%Not measuredOnly GPT-5.6 Luna measured
CorpFin (Vals AI)64.2%Not measuredOnly GPT-5.6 Luna measured
TaxEval (Vals AI)76.2%Not measuredOnly GPT-5.6 Luna measured
MortgageTax (Vals AI)67.3%Not measuredOnly GPT-5.6 Luna measured
MedCode (Vals AI)42.4%48.5%GPT-6 Astra
SimpleQA Verified41.0%75.6%GPT-6 Astra
LMArena Text: science14331451GPT-6 Astra
LMArena Text: medicine and healthcare13991425GPT-6 Astra
LMArena Text: legal and government14461462GPT-6 Astra
LMArena Text: business and finance14391439GPT-6 Astra
Neither model has a result on the other 6 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index09
Web design benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
Design Arena: websites12561337GPT-6 Astra
Design Arena: UI components12501394GPT-6 Astra
Design Arena: game dev11961474GPT-6 Astra
Design Arena: data viz12121335GPT-6 Astra
Design Arena: 3D11211501GPT-6 Astra
Design Arena: all code categories12311379GPT-6 Astra
Design Arena: SVG11931431GPT-6 Astra
Design Arena: ASCII art11441359GPT-6 Astra
LiveBench design76.0%82.0%GPT-6 Astra
GeneralLike-for-likePublic boards, shown as published, kept out of the index425
General benchmarks for GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
Vals IndexNot measured65.0%Only GPT-6 Astra measured
LiveBench data analysis78.0%83.0%GPT-6 Astra
Public Benefits Bench (Vals AI)61.2%Not measuredOnly GPT-5.6 Luna measured
SAGE (Vals AI)44.2%46.4%GPT-6 Astra
MedScribe (Vals AI)84.4%87.9%GPT-6 Astra
Vals Multimodal Index69.1%Not measuredOnly GPT-5.6 Luna measured
Long context reasoning (AA-LCR)83.7%80.7%GPT-5.6 Luna
DTBench89.1%97.3%GPT-6 Astra
LMCA48.5%64.4%GPT-6 Astra
Surface Evolver Bench61.9%Not measuredOnly GPT-5.6 Luna measured
Furniture assembly42.5%80.0%GPT-6 Astra
LMArena Text14311441GPT-6 Astra
LMArena Text: instruction following14371455GPT-6 Astra
LMArena Text: creative writing13961420GPT-6 Astra
LMArena Vision12571280GPT-6 Astra
LMArena Text: English14411447GPT-6 Astra
LMArena Text: non-English14171432GPT-6 Astra
LMArena Text: Chinese14701489GPT-6 Astra
LMArena Text: German14551459GPT-6 Astra
LMArena Text: Japanese14151405GPT-5.6 Luna
LMArena Text: Korean14151428GPT-6 Astra
LMArena Text: French14581432GPT-5.6 Luna
LMArena Text: Spanish14461422GPT-5.6 Luna
LMArena Text: Russian14271438GPT-6 Astra
LMArena Text: Polish14051422GPT-6 Astra
LMArena Text: multi-turn14341447GPT-6 Astra
LMArena Text: longer queries14361460GPT-6 Astra
LMArena Text: writing and language14191437GPT-6 Astra
LMArena Text: entertainment and media14021427GPT-6 Astra
LMArena Vision: English12631280GPT-6 Astra
LMArena Vision: Chinese12941361GPT-6 Astra
LMArena Vision: reading text12641292GPT-6 Astra
LMArena Vision: humor1190Not measuredOnly GPT-5.6 Luna measured
LMArena Vision: creative writing12571286GPT-6 Astra
LMArena Document1457Not measuredOnly GPT-5.6 Luna measured
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 GPT-5.6 Luna and GPT-6 Astra
BenchmarkGPT-5.6 LunaGPT-6 AstraLeader
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

GPT-5.6 Luna$0.0008Fits in one request
GPT-6 Astra$0.035Fits in one request

GPT-5.6 Luna costs less

Repository review

50K input + 3K output tokens

GPT-5.6 Luna$0.014Fits in one request
GPT-6 Astra$0.650Fits in one request

GPT-5.6 Luna costs less

Agent loop

200K input + 10K output tokens

GPT-5.6 Luna$0.052Fits in one request
GPT-6 Astra$2.50Fits 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 GPT-5.6 Luna and GPT-6 Astra
SpecificationOpenAI GPT-5.6 LunaOpenAI GPT-6 Astra
MakerOpenAIOpenAI
WeightsNo public weights listedNo public weights listed
ReleasedJuly 9, 2026September 4, 2026
Context window1.05M1.05M
Input $/Mtok$0.20$10.00
Output $/Mtok$1.20$50.00
Coding index61.588.7
Independent measurements behind it22
Cost per solved task$0.04Not computable
SourceOpenRouter listingOpenRouter listing

Questions

Is GPT-5.6 Luna better than GPT-6 Astra for coding?

Pick GPT-6 Astra for coding: it scores 88.7 on the Vibe Coding Index against 61.5 for GPT-5.6 Luna. Pick GPT-5.6 Luna when output tokens cost 41.7x less, or when what matters is CyberBench (Vals AI) or Finance Agent (Vals AI), where it leads.

Which is cheaper, GPT-5.6 Luna or GPT-6 Astra?

GPT-5.6 Luna costs $0.20 per million input tokens and $1.20 per million output tokens; GPT-6 Astra costs $10.00 and $50.00. Cost per solved task is known for GPT-5.6 Luna only.

Which has the bigger context window, GPT-5.6 Luna or GPT-6 Astra?

Neither: both take 1.05M tokens.

How many benchmarks is the GPT-5.6 Luna vs GPT-6 Astra comparison based on?

101 benchmarks have a result for both models as of October 21, 2026. GPT-5.6 Luna's coding index rests on 2 independent benchmarks and GPT-6 Astra's on 2. Where only one model has a result, the page says so instead of naming a winner.

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