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GPT-5.6 Luna vs Grok 4.3

GPT-5.6 Luna leads Grok 4.3 on coding, 58.0 to 37.4 on the Vibe Coding Index, and GPT-5.6 Luna costs 2.1x less per output token ($1.20 vs $2.50 per million). Updated October 22, 2026; 89 benchmarks have a result for both.

Replace GPT-5.6 Luna Replace Grok 4.3
GPT-5.6 LunaOpenAI
Coding
58.0
Overall
61.6
Output $/M
$1.20
83
Grok 4.3xAI
Coding
37.4
Overall
53.1
Output $/M
$2.50
5
vs boards won of 89 shared, 1 tied

GPT-5.6 Luna or Grok 4.3: which to pick

Pick GPT-5.6 Luna for coding: it scores 58.0 on the Vibe Coding Index against 37.4 for Grok 4.3.

Pick Grok 4.3 for work measured by LegalBench (Vals AI) or CorpFin (Vals AI), where it leads.

Model AGPT-5.6 LunaOpenAI58.0/1006 independent benchmarks$0.04 per solved taskModel BGrok 4.3xAI37.4/1003 independent benchmarks$0.31 per solved task
Shared results
89
GPT-5.6 Luna only
30
Grok 4.3 only
16
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
GPT-5.6 Luna 58.0 from 6 benchmarks, Grok 4.3 37.4 from 3 benchmarks.
Widest category
Math, 27.3 points apart on average over 6 shared benchmarks.
Widest single gap
Vibe Code Bench (Vals AI): GPT-5.6 Luna 77.1% against Grok 4.3 19.4%, 57.7 points apart on a 0 to 100 scale.
Output price
GPT-5.6 Luna $1.20 against Grok 4.3 $2.50 per million output tokens, 2.1x apart.
Context window
GPT-5.6 Luna takes 1.05M tokens, Grok 4.3 1M.

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 LunaBarsGrok 4.3Ties
Coding1501 tie
Intelligence10
Agentic work60
Reasoning110
Math60
Knowledge92
Web design71
General282
All shared boards8351 tie
CodingLike-for-likeSix of these boards feed the Vibe Coding Index150
Coding benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
LiveBench coding73.6%Not measuredOnly GPT-5.6 Luna measured
LMArena WebDev15181358GPT-5.6 Luna
AA Coding Index71.442.2GPT-5.6 Luna
LiveCodeBench (Vals AI)Not measured84.5%Only Grok 4.3 measured
SWE-bench Verified (Vals AI)93.0%71.4%GPT-5.6 Luna
Terminal-Bench 4 (Vals AI)11.6%Not measuredOnly GPT-5.6 Luna measured
Vibe Code Bench (Vals AI)77.1%19.4%GPT-5.6 Luna
Code migration (Vals AI)44.5%6.8%GPT-5.6 Luna
ProgramBench (Vals AI)0.0%0.0%Tie
IOI (Vals AI)61.8%Not measuredOnly GPT-5.6 Luna measured
Terminal-Bench 2.1 (Vals AI)79.0%42.0%GPT-5.6 Luna
Vibe Code Bench 1-100 (Vals AI)22.6%Not measuredOnly GPT-5.6 Luna measured
SkillsBench (Vals AI)60.5%40.6%GPT-5.6 Luna
CyberBench (Vals AI)73.6%Not measuredOnly GPT-5.6 Luna measured
SciCode53.6%48.3%GPT-5.6 Luna
Terminal-Bench Hard (Artificial Analysis run)Not measured37.9%Only Grok 4.3 measured
FrontierCode39.8%Not measuredOnly GPT-5.6 Luna measured
WeirdML60.9%49.9%GPT-5.6 Luna
ALE-Bench1667.4944.2GPT-5.6 Luna
LMArena Text: coding14661415GPT-5.6 Luna
LMArena Text: software and IT14631416GPT-5.6 Luna
LMArena WebDev: React15081353GPT-5.6 Luna
LMArena WebDev: HTML15201367GPT-5.6 Luna
LMArena WebDev: from an image15171375GPT-5.6 Luna
SciCode6.2%Not measuredOnly GPT-5.6 Luna measured
Neither model has a result on the other 14 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index10
Intelligence benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
AA Intelligence Index37.324.9GPT-5.6 Luna
Epoch Capabilities Index156.5Not measuredOnly GPT-5.6 Luna measured
Agentic workLike-for-likePublic boards, shown as published, kept out of the index60
Agentic work benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
AA Agentic Index42.115.5GPT-5.6 Luna
Design Arena: agents building web appsNot measured1126Only Grok 4.3 measured
Design Arena: agents building full-stack appsNot measured1006Only Grok 4.3 measured
Design Arena: agents building mobile appsNot measured1058Only Grok 4.3 measured
Design Arena: agents building Android appsNot measured962Only Grok 4.3 measured
Design Arena: agents building Godot gamesNot measured914Only Grok 4.3 measured
Design Arena: agents building gamesNot measured1007Only Grok 4.3 measured
Design Arena: HTML slidesNot measured959Only Grok 4.3 measured
Design Arena: PowerPoint slidesNot measured989Only Grok 4.3 measured
Design Arena: spreadsheetsNot measured927Only Grok 4.3 measured
LiveBench research51.0%Not measuredOnly GPT-5.6 Luna measured
LiveBench browser68.0%Not measuredOnly GPT-5.6 Luna measured
LiveBench long agentic30.4%Not measuredOnly GPT-5.6 Luna measured
SREBench (Vals AI)1.5%Not measuredOnly GPT-5.6 Luna measured
Finance Agent (Vals AI)55.0%37.7%GPT-5.6 Luna
Tax Agent Bench (Vals AI)24.8%6.2%GPT-5.6 Luna
Legal Research Bench (Vals AI)36.5%15.4%GPT-5.6 Luna
Excel Modeling Benchmark (Vals AI)67.1%18.4%GPT-5.6 Luna
BioMysteryBench (Vals AI)61.5%Not measuredOnly GPT-5.6 Luna measured
Terminal-Bench-Science (Vals AI)0.0%Not measuredOnly GPT-5.6 Luna measured
Vals Science Index25.3%Not measuredOnly GPT-5.6 Luna measured
τ²-Bench TelecomNot measured97.7%Only Grok 4.3 measured
APEX-Agents43.0%Not measuredOnly GPT-5.6 Luna measured
BALROG45.6%Not measuredOnly GPT-5.6 Luna measured
Vending-Bench 2$4,095$35GPT-5.6 Luna
LMArena SearchNot measured1166Only Grok 4.3 measured
Neither model has a result on the other 15 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index110
Reasoning benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
GPQA Diamond91.7%91.4%GPT-5.6 Luna
LiveBench reasoning85.6%Not measuredOnly GPT-5.6 Luna measured
MysteryMechanism (Vals AI)14.4%Not measuredOnly GPT-5.6 Luna measured
MMMU Pro (Vals AI)85.0%83.1%GPT-5.6 Luna
GPQA Diamond (Artificial Analysis run)91.1%90.1%GPT-5.6 Luna
Humanity's Last Exam (Artificial Analysis run)39.5%37.2%GPT-5.6 Luna
GPQA Diamond (Epoch AI run)91.6%88.8%GPT-5.6 Luna
ARC-AGI88.0%Not measuredOnly GPT-5.6 Luna measured
ARC-AGI-259.5%Not measuredOnly GPT-5.6 Luna measured
SimpleBench46.8%Not measuredOnly GPT-5.6 Luna measured
Chess puzzles43.0%18.0%GPT-5.6 Luna
Mystery game puzzles21.0%Not measuredOnly GPT-5.6 Luna measured
LMArena Text: hard prompts14511396GPT-5.6 Luna
LMArena Text: expert14781384GPT-5.6 Luna
LMArena Text: hard prompts in English14601402GPT-5.6 Luna
LMArena Vision: diagrams12731241GPT-5.6 Luna
LMArena Vision: homework12821241GPT-5.6 Luna
Kagi LLM Benchmark49.1%Not measuredOnly GPT-5.6 Luna measured
Neither model has a result on the other 4 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index60
Math benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
OTIS Mock AIME98.3%93.3%GPT-5.6 Luna
FrontierMath, tiers 1 to 382.1%42.8%GPT-5.6 Luna
FrontierMath, tier 461.0%14.6%GPT-5.6 Luna
ProofBench60.0%11.0%GPT-5.6 Luna
LMArena Text: math14591387GPT-5.6 Luna
LMArena Text: mathematical work14701396GPT-5.6 Luna
Neither model has a result on the other 7 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index92
Knowledge benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
MMLU Pro86.0%85.8%GPT-5.6 Luna
LegalBench (Vals AI)84.0%84.5%Grok 4.3
CaseLaw (Vals AI)Not measured79.3%Only Grok 4.3 measured
CorpFin (Vals AI)64.2%68.5%Grok 4.3
TaxEval (Vals AI)76.2%70.8%GPT-5.6 Luna
MortgageTax (Vals AI)67.3%48.3%GPT-5.6 Luna
MedCode (Vals AI)42.4%38.1%GPT-5.6 Luna
SimpleQA Verified41.0%33.2%GPT-5.6 Luna
LMArena Text: science14331399GPT-5.6 Luna
LMArena Text: medicine and healthcare13991384GPT-5.6 Luna
LMArena Text: legal and government14461386GPT-5.6 Luna
LMArena Text: business and finance14391381GPT-5.6 Luna
FACTS Benchmark Suite35.0%Not measuredOnly GPT-5.6 Luna measured
Neither model has a result on the other 5 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index71
Web design benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
Design Arena: websites12551196GPT-5.6 Luna
Design Arena: UI components12481190GPT-5.6 Luna
Design Arena: game dev11951173GPT-5.6 Luna
Design Arena: data viz12121180GPT-5.6 Luna
Design Arena: 3D11211124Grok 4.3
Design Arena: all code categories12301186GPT-5.6 Luna
Design Arena: SVG11931080GPT-5.6 Luna
Design Arena: ASCII art11421125GPT-5.6 Luna
LiveBench design76.0%Not measuredOnly GPT-5.6 Luna measured
GeneralLike-for-likePublic boards, shown as published, kept out of the index282
General benchmarks for GPT-5.6 Luna and Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
LiveBench data analysis78.0%Not measuredOnly GPT-5.6 Luna measured
Public Benefits Bench (Vals AI)61.2%51.7%GPT-5.6 Luna
SAGE (Vals AI)44.2%19.7%GPT-5.6 Luna
MedScribe (Vals AI)84.4%74.4%GPT-5.6 Luna
Vals Multimodal Index69.1%43.3%GPT-5.6 Luna
IFBenchNot measured83.3%Only Grok 4.3 measured
Long context reasoning (AA-LCR)83.7%75.0%GPT-5.6 Luna
DTBench89.1%90.7%Grok 4.3
LMCA48.5%38.3%GPT-5.6 Luna
Surface Evolver Bench61.9%Not measuredOnly GPT-5.6 Luna measured
Furniture assembly42.5%Not measuredOnly GPT-5.6 Luna measured
LMArena Text14311397GPT-5.6 Luna
LMArena Text: instruction following14371366GPT-5.6 Luna
LMArena Text: creative writing13961380GPT-5.6 Luna
LMArena Vision12571229GPT-5.6 Luna
LMArena Text: English14411404GPT-5.6 Luna
LMArena Text: non-English14171385GPT-5.6 Luna
LMArena Text: Chinese14701422GPT-5.6 Luna
LMArena Text: German14551395GPT-5.6 Luna
LMArena Text: Japanese14151379GPT-5.6 Luna
LMArena Text: Korean14151354GPT-5.6 Luna
LMArena Text: French14581411GPT-5.6 Luna
LMArena Text: Spanish14461399GPT-5.6 Luna
LMArena Text: Russian14271399GPT-5.6 Luna
LMArena Text: Polish14051398GPT-5.6 Luna
LMArena Text: multi-turn14341406GPT-5.6 Luna
LMArena Text: longer queries14361393GPT-5.6 Luna
LMArena Text: writing and language14191385GPT-5.6 Luna
LMArena Text: entertainment and media14021370GPT-5.6 Luna
LMArena Vision: English12631235GPT-5.6 Luna
LMArena Vision: Chinese12941257GPT-5.6 Luna
LMArena Vision: reading text12641235GPT-5.6 Luna
LMArena Vision: humor11901222Grok 4.3
LMArena Vision: recognizing thingsNot measured1217Only Grok 4.3 measured
LMArena Vision: creative writing12571237GPT-5.6 Luna
LMArena Document1457Not measuredOnly GPT-5.6 Luna measured
Neither model has a result on the other 10 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 Grok 4.3
BenchmarkGPT-5.6 LunaGrok 4.3Leader
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
Grok 4.3$0.0025Fits 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
Grok 4.3$0.070Fits 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
Grok 4.3$0.275Fits 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 Grok 4.3
SpecificationOpenAI GPT-5.6 LunaSpaceXAI Grok 4.3
MakerOpenAIxAI
WeightsNo public weights listedNo public weights listed
ReleasedJuly 9, 2026April 30, 2026
Context window1.05M1M
Input $/Mtok$0.20$1.25
Output $/Mtok$1.20$2.50
Coding index58.037.4
Independent measurements behind it63
Cost per solved task$0.04$0.31
SourceOpenRouter listingOpenRouter listing

Questions

Is GPT-5.6 Luna better than Grok 4.3 for coding?

Pick GPT-5.6 Luna for coding: it scores 58.0 on the Vibe Coding Index against 37.4 for Grok 4.3. Pick Grok 4.3 for work measured by LegalBench (Vals AI) or CorpFin (Vals AI), where it leads.

Which is cheaper, GPT-5.6 Luna or Grok 4.3?

GPT-5.6 Luna costs $0.20 per million input tokens and $1.20 per million output tokens; Grok 4.3 costs $1.25 and $2.50. Per solved SWE-bench Verified task, GPT-5.6 Luna costs $0.04 and Grok 4.3 $0.31.

Which has the bigger context window, GPT-5.6 Luna or Grok 4.3?

GPT-5.6 Luna, with 1.05M tokens against 1M.

How many benchmarks is the GPT-5.6 Luna vs Grok 4.3 comparison based on?

89 benchmarks have a result for both models as of October 22, 2026. GPT-5.6 Luna's coding index rests on 6 independent benchmarks and Grok 4.3's on 3. Where only one model has a result, the page says so instead of naming a winner.

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