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GPT-5.3-Codex vs Kimi K3

Updated October 21, 2026. 28 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace GPT-5.3-Codex Replace Kimi K3
GPT-5.3-CodexOpenAI
Coding
29.5
Overall
32.5
Output $/M
$14.00
4
Kimi K3Moonshot AI
Coding
61.8
Overall
43.6
Output $/M
$11.936
24
vs boards won of 28 shared

Decision reading

Pick Kimi K3 for coding: it scores 61.8 on the Vibe Coding Index against 29.5 for GPT-5.3-Codex.

Pick GPT-5.3-Codex when a solved task costs $0.59 against $0.81, or when what matters is LiveCodeBench (Vals AI) or IOI (Vals AI), where it leads.

Model AGPT-5.3-CodexOpenAI29.5/1001 independent benchmark$0.59 per solved taskModel BKimi K3Moonshot AI61.8/1002 independent benchmarks$0.81 per solved task
Shared results
28
GPT-5.3-Codex only
6
Kimi K3 only
89
Like-for-like categories
6 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-5.3-Codex 29.5 from 1 benchmark, Kimi K3 61.8 from 2 benchmarks.
Widest category
Web design, 27.4 points apart on average over 7 shared benchmarks.
Widest single gap
Design Arena: 3D: GPT-5.3-Codex 1008 against Kimi K3 1388, 47.5 points apart on a 0 to 100 scale.
Output price
GPT-5.3-Codex $14.00 against Kimi K3 $11.936 per million output tokens, 1.2x apart.
Context window
GPT-5.3-Codex takes 400K tokens, Kimi K3 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
CategoryGPT-5.3-CodexBarsKimi K3Ties
Coding37
Intelligence02
Agentic work15
Reasoning02
Web design07
General01
All shared boards424
CodingLike-for-likeFour of these boards feed the Vibe Coding Index37
Coding benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
LiveBench codingNot measured59.3%Only Kimi K3 measured
LMArena WebDev14071655Kimi K3
AA Coding IndexNot measured76.2Only Kimi K3 measured
LiveCodeBench (Vals AI)87.3%87.2%GPT-5.3-Codex
SWE-bench Verified (Vals AI)78.0%93.4%Kimi K3
Terminal-Bench 4 (Vals AI)Not measured17.2%Only Kimi K3 measured
Vibe Code Bench (Vals AI)61.8%85.0%Kimi K3
Code migration (Vals AI)Not measured16.1%Only Kimi K3 measured
ProgramBench (Vals AI)Not measured2.0%Only Kimi K3 measured
IOI (Vals AI)53.8%48.9%GPT-5.3-Codex
Terminal-Bench 2.1 (Vals AI)Not measured80.9%Only Kimi K3 measured
SWE-bench Multimodal (Vals AI)Not measured44.2%Only Kimi K3 measured
Vibe Code Bench 1-100 (Vals AI)Not measured18.2%Only Kimi K3 measured
CyberBench (Vals AI)Not measured75.2%Only Kimi K3 measured
SciCodeNot measured59.5%Only Kimi K3 measured
Terminal-Bench Hard (Artificial Analysis run)53.0%Not measuredOnly GPT-5.3-Codex measured
Terminal-Bench78.4%Not measuredOnly GPT-5.3-Codex measured
FrontierCodeNot measured44.2%Only Kimi K3 measured
FrontierSWENot measured25.9%Only Kimi K3 measured
WeirdML79.3%82.6%Kimi K3
ALE-Bench1655.21524.5GPT-5.3-Codex
LMArena Text: codingNot measured1508Only Kimi K3 measured
LMArena Text: software and ITNot measured1499Only Kimi K3 measured
LMArena WebDev: React13951670Kimi K3
LMArena WebDev: HTML14221644Kimi K3
LMArena WebDev: from an image14431579Kimi K3
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-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
AA Intelligence Index32.543.6Kimi K3
Epoch Capabilities Index157.1157.9Kimi K3
Agentic workLike-for-likePublic boards, shown as published, kept out of the index15
Agentic work benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
AA Agentic IndexNot measured50.0Only Kimi K3 measured
Design Arena: agents building web apps10331296Kimi K3
Design Arena: agents building full-stack apps9831315Kimi K3
Design Arena: agents building mobile apps10541267Kimi K3
Design Arena: agents building Android apps10841256Kimi K3
Design Arena: agents building Godot games11241223Kimi K3
Design Arena: agents building gamesNot measured1252Only Kimi K3 measured
Design Arena: HTML slidesNot measured1256Only Kimi K3 measured
Design Arena: PowerPoint slidesNot measured1273Only Kimi K3 measured
Design Arena: spreadsheetsNot measured1058Only Kimi K3 measured
LiveBench researchNot measured79.0%Only Kimi K3 measured
LiveBench browserNot measured16.0%Only Kimi K3 measured
LiveBench long agenticNot measured42.8%Only Kimi K3 measured
Finance Agent (Vals AI)Not measured53.1%Only Kimi K3 measured
Tax Agent Bench (Vals AI)Not measured33.4%Only Kimi K3 measured
Legal Research Bench (Vals AI)Not measured46.1%Only Kimi K3 measured
Harvey's Legal Agent Benchmark (Vals AI)Not measured12.9%Only Kimi K3 measured
Excel Modeling Benchmark (Vals AI)Not measured66.7%Only Kimi K3 measured
BioMysteryBench (Vals AI)Not measured72.6%Only Kimi K3 measured
Terminal-Bench-Science (Vals AI)Not measured1.4%Only Kimi K3 measured
Time Horizon Index (Vals AI)Not measured10.5%Only Kimi K3 measured
τ²-Bench Telecom86.0%Not measuredOnly GPT-5.3-Codex measured
APEX-AgentsNot measured47.8%Only Kimi K3 measured
METR time horizons74.5%Not measuredOnly GPT-5.3-Codex measured
PostTrainBenchNot measured32.0%Only Kimi K3 measured
Vending-Bench 2$5,940$5,165GPT-5.3-Codex
Neither model has a result on the other 13 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index02
Reasoning benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
GPQA DiamondNot measured92.9%Only Kimi K3 measured
LiveBench reasoningNot measured90.7%Only Kimi K3 measured
MMMU Pro (Vals AI)Not measured88.2%Only Kimi K3 measured
GPQA Diamond (Artificial Analysis run)91.5%93.5%Kimi K3
Humanity's Last Exam (Artificial Analysis run)42.5%46.9%Kimi K3
GPQA Diamond (Epoch AI run)Not measured93.1%Only Kimi K3 measured
ARC-AGINot measured94.5%Only Kimi K3 measured
ARC-AGI-2Not measured60.4%Only Kimi K3 measured
SimpleBenchNot measured60.7%Only Kimi K3 measured
Chess puzzlesNot measured37.0%Only Kimi K3 measured
Mystery game puzzlesNot measured26.0%Only Kimi K3 measured
LMArena Text: hard promptsNot measured1495Only Kimi K3 measured
LMArena Text: expertNot measured1520Only Kimi K3 measured
LMArena Text: hard prompts in EnglishNot measured1496Only Kimi K3 measured
Neither model has a result on the other 7 boards here
MathDirectional onlyPublic boards, shown as published, kept out of the index6 boards, none shared
Math benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
OTIS Mock AIMENot measured97.2%Only Kimi K3 measured
FrontierMath, tiers 1 to 3Not measured72.2%Only Kimi K3 measured
FrontierMath, tier 4Not measured39.0%Only Kimi K3 measured
ProofBenchNot measured87.0%Only Kimi K3 measured
LMArena Text: mathNot measured1494Only Kimi K3 measured
LMArena Text: mathematical workNot measured1505Only Kimi K3 measured
Neither model has a result on the other 7 boards here
KnowledgeDirectional onlyPublic boards, shown as published, kept out of the index11 boards, none shared
Knowledge benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
MMLU ProNot measured88.0%Only Kimi K3 measured
LegalBench (Vals AI)Not measured86.2%Only Kimi K3 measured
CorpFin (Vals AI)Not measured71.6%Only Kimi K3 measured
TaxEval (Vals AI)Not measured75.7%Only Kimi K3 measured
MortgageTax (Vals AI)Not measured66.3%Only Kimi K3 measured
MedCode (Vals AI)Not measured49.4%Only Kimi K3 measured
SimpleQA VerifiedNot measured50.6%Only Kimi K3 measured
LMArena Text: scienceNot measured1508Only Kimi K3 measured
LMArena Text: medicine and healthcareNot measured1489Only Kimi K3 measured
LMArena Text: legal and governmentNot measured1503Only Kimi K3 measured
LMArena Text: business and financeNot measured1470Only Kimi K3 measured
Neither model has a result on the other 6 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index07
Web design benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
Design Arena: websites11631336Kimi K3
Design Arena: UI components11371345Kimi K3
Design Arena: game dev11621361Kimi K3
Design Arena: data viz11641350Kimi K3
Design Arena: 3D10081388Kimi K3
Design Arena: all code categories11451361Kimi K3
Design Arena: SVG11291301Kimi K3
Design Arena: ASCII art1151Not measuredOnly GPT-5.3-Codex measured
LiveBench designNot measured77.2%Only Kimi K3 measured
GeneralLike-for-likePublic boards, shown as published, kept out of the index01
General benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
Vals IndexNot measured53.0%Only Kimi K3 measured
LiveBench data analysisNot measured78.7%Only Kimi K3 measured
Public Benefits Bench (Vals AI)Not measured68.2%Only Kimi K3 measured
SAGE (Vals AI)Not measured52.8%Only Kimi K3 measured
MedScribe (Vals AI)Not measured88.0%Only Kimi K3 measured
Vals Multimodal IndexNot measured73.4%Only Kimi K3 measured
IFBench75.4%Not measuredOnly GPT-5.3-Codex measured
Long context reasoning (AA-LCR)83.3%88.7%Kimi K3
DTBenchNot measured91.2%Only Kimi K3 measured
LMCANot measured52.7%Only Kimi K3 measured
Surface Evolver BenchNot measured95.0%Only Kimi K3 measured
Furniture assemblyNot measured34.2%Only Kimi K3 measured
LMArena TextNot measured1476Only Kimi K3 measured
LMArena Text: instruction followingNot measured1485Only Kimi K3 measured
LMArena Text: creative writingNot measured1457Only Kimi K3 measured
LMArena Text: EnglishNot measured1481Only Kimi K3 measured
LMArena Text: non-EnglishNot measured1466Only Kimi K3 measured
LMArena Text: ChineseNot measured1529Only Kimi K3 measured
LMArena Text: GermanNot measured1490Only Kimi K3 measured
LMArena Text: JapaneseNot measured1494Only Kimi K3 measured
LMArena Text: KoreanNot measured1460Only Kimi K3 measured
LMArena Text: FrenchNot measured1492Only Kimi K3 measured
LMArena Text: SpanishNot measured1472Only Kimi K3 measured
LMArena Text: RussianNot measured1485Only Kimi K3 measured
LMArena Text: PolishNot measured1458Only Kimi K3 measured
LMArena Text: multi-turnNot measured1489Only Kimi K3 measured
LMArena Text: longer queriesNot measured1494Only Kimi K3 measured
LMArena Text: writing and languageNot measured1471Only Kimi K3 measured
LMArena Text: entertainment and mediaNot measured1453Only Kimi K3 measured
Neither model has a result on the other 17 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for GPT-5.3-Codex and Kimi K3
BenchmarkGPT-5.3-CodexKimi K3Leader
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-5.3-Codex$0.0088Fits in one request
Kimi K3$0.0062Fits in one request

Kimi K3 costs less

Repository review

50K input + 3K output tokens

GPT-5.3-Codex$0.130Fits in one request
Kimi K3$0.048Fits in one request

Kimi K3 costs less

Agent loop

200K input + 10K output tokens

GPT-5.3-Codex$0.490Fits in one request
Kimi K3$0.167Fits in one request

Kimi K3 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-5.3-Codex and Kimi K3
SpecificationOpenAI GPT-5.3-CodexMoonshotAI Kimi K3
MakerOpenAIMoonshot AI
WeightsNo public weights listedOpen weights
ReleasedFebruary 24, 2026July 16, 2026
Context window400K1.05M
Input $/Mtok$1.75$0.239
Output $/Mtok$14.00$11.936
Coding index29.561.8
Independent measurements behind it12
Cost per solved task$0.59$0.81
SourceOpenRouter listingOpenRouter listing

Questions

Is GPT-5.3-Codex better than Kimi K3 for coding?

Pick Kimi K3 for coding: it scores 61.8 on the Vibe Coding Index against 29.5 for GPT-5.3-Codex. Pick GPT-5.3-Codex when a solved task costs $0.59 against $0.81, or when what matters is LiveCodeBench (Vals AI) or IOI (Vals AI), where it leads.

Which is cheaper, GPT-5.3-Codex or Kimi K3?

GPT-5.3-Codex costs $1.75 per million input tokens and $14.00 per million output tokens; Kimi K3 costs $0.239 and $11.936. Per solved SWE-bench Verified task, GPT-5.3-Codex costs $0.59 and Kimi K3 $0.81.

Which has the bigger context window, GPT-5.3-Codex or Kimi K3?

Kimi K3, with 1.05M tokens against 400K.

How many benchmarks is the GPT-5.3-Codex vs Kimi K3 comparison based on?

28 benchmarks have a result for both models as of October 21, 2026. GPT-5.3-Codex's coding index rests on 1 independent benchmark and Kimi K3's on 2. Where only one model has a result, the page says so instead of naming a winner.

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