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GPT-5.1-Codex vs o3

Updated October 21, 2026. 19 benchmarks have a result for both. Coding is ranked on the Vibe Coding Index; every other board is shown as published.

Replace GPT-5.1-Codex Replace o3
GPT-5.1-CodexOpenAI
Coding
50.5
Overall
23.7
Output $/M
$10.00
16
o3OpenAI
Coding
70.7
Overall
20.2
Output $/M
$8.00
3
vs boards won of 19 shared

Decision reading

Pick o3 for coding: it scores 70.7 on the Vibe Coding Index against 50.5 for GPT-5.1-Codex.

Pick GPT-5.1-Codex when the context window is larger, 400K against 200K tokens, or when what matters is SWE-bench Verified or LiveCodeBench (Vals AI), where it leads.

Model AGPT-5.1-CodexOpenAI50.5/1002 independent benchmarks$0.892 per solved taskModel Bo3OpenAI70.7/1002 independent benchmarks$0.571 per solved task
Shared results
19
GPT-5.1-Codex only
7
o3 only
78
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-5.1-Codex 50.5 from 2 benchmarks, o3 70.7 from 2 benchmarks.
Widest category
Web design, 14.9 points apart on average over 5 shared benchmarks.
Widest single gap
Design Arena: UI components: GPT-5.1-Codex 1237 against o3 1016, 27.6 points apart on a 0 to 100 scale.
Output price
GPT-5.1-Codex $10.00 against o3 $8.00 per million output tokens, 1.3x apart.
Context window
GPT-5.1-Codex takes 400K tokens, o3 200K.

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-5.1-CodexBarso3Ties
Coding41
Intelligence10
Agentic work10
Reasoning20
Math20
Knowledge10
Web design50
General02
All shared boards163
CodingLike-for-likeFour of these boards feed the Vibe Coding Index41
Coding benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
Aider polyglotNot measured81.3%Only o3 measured
SWE-bench Verified66.0%58.4%GPT-5.1-Codex
SWE-bench MultimodalNot measured36.0%Only o3 measured
LMArena WebDev1337Not measuredOnly GPT-5.1-Codex measured
LiveCodeBench (Vals AI)85.5%83.9%GPT-5.1-Codex
Vibe Code Bench (Vals AI)13.1%Not measuredOnly GPT-5.1-Codex measured
LiveCodeBench (Artificial Analysis run)84.9%80.8%GPT-5.1-Codex
Terminal-Bench Hard (Artificial Analysis run)34.8%37.1%o3
Terminal-Bench57.8%Not measuredOnly GPT-5.1-Codex measured
GSO-BenchNot measured8.8%Only o3 measured
WeirdMLNot measured52.4%Only o3 measured
ALE-Bench1244.9933.5GPT-5.1-Codex
LMArena Text: codingNot measured1407Only o3 measured
LMArena Text: software and ITNot measured1415Only o3 measured
LMArena WebDev: HTML1346Not measuredOnly GPT-5.1-Codex measured
Neither model has a result on the other 23 boards here
IntelligenceLike-for-likePublic boards, shown as published, kept out of the index10
Intelligence benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
AA Intelligence Index23.720.2GPT-5.1-Codex
Epoch Capabilities IndexNot measured146.7Only o3 measured
Agentic workLike-for-likePublic boards, shown as published, kept out of the index10
Agentic work benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
Design Arena: agents building web apps1018Not measuredOnly GPT-5.1-Codex measured
Design Arena: agents building full-stack apps1086Not measuredOnly GPT-5.1-Codex measured
Design Arena: agents building mobile apps1191Not measuredOnly GPT-5.1-Codex measured
τ²-Bench Telecom83.0%80.7%GPT-5.1-Codex
METR time horizonsNot measured65.4%Only o3 measured
GDPvalNot measured30.8%Only o3 measured
DeepResearch BenchNot measured45.2%Only o3 measured
OSWorldNot measured23.0%Only o3 measured
Neither model has a result on the other 31 boards here
ReasoningLike-for-likePublic boards, shown as published, kept out of the index20
Reasoning benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
GPQA DiamondNot measured84.1%Only o3 measured
MMMU Pro (Vals AI)Not measured80.4%Only o3 measured
GPQA Diamond (Artificial Analysis run)86.0%82.7%GPT-5.1-Codex
Humanity's Last Exam (Artificial Analysis run)25.7%20.1%GPT-5.1-Codex
GPQA Diamond (Epoch AI run)Not measured81.8%Only o3 measured
ARC-AGINot measured60.8%Only o3 measured
ARC-AGI-2Not measured6.5%Only o3 measured
SimpleBenchNot measured53.1%Only o3 measured
Chess puzzlesNot measured37.0%Only o3 measured
Mystery game puzzlesNot measured29.0%Only o3 measured
VPCTNot measured52.0%Only o3 measured
LMArena Text: hard promptsNot measured1402Only o3 measured
LMArena Text: expertNot measured1402Only o3 measured
LMArena Text: hard prompts in EnglishNot measured1411Only o3 measured
LMArena Vision: diagramsNot measured1220Only o3 measured
LMArena Vision: homeworkNot measured1234Only o3 measured
Neither model has a result on the other 5 boards here
MathLike-for-likePublic boards, shown as published, kept out of the index20
Math benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
AIMENot measured85.3%Only o3 measured
MATH 500 (Vals AI)Not measured94.6%Only o3 measured
MGSM (Vals AI)Not measured91.8%Only o3 measured
AA Math Index95.788.3GPT-5.1-Codex
AIME 2025 (Artificial Analysis run)95.7%88.3%GPT-5.1-Codex
OTIS Mock AIMENot measured84.4%Only o3 measured
FrontierMath, tiers 1 to 3Not measured33.3%Only o3 measured
MATH level 5Not measured97.8%Only o3 measured
LMArena Text: mathNot measured1426Only o3 measured
LMArena Text: mathematical workNot measured1423Only o3 measured
Neither model has a result on the other 3 boards here
KnowledgeLike-for-likePublic boards, shown as published, kept out of the index10
Knowledge benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
MMLU ProNot measured85.6%Only o3 measured
LegalBench (Vals AI)Not measured83.8%Only o3 measured
CorpFin (Vals AI)Not measured59.7%Only o3 measured
TaxEval (Vals AI)Not measured74.6%Only o3 measured
MortgageTax (Vals AI)Not measured65.7%Only o3 measured
MedQA (Vals AI)Not measured96.1%Only o3 measured
MedCode (Vals AI)Not measured47.3%Only o3 measured
MMLU Pro (Artificial Analysis run)86.0%85.3%GPT-5.1-Codex
SimpleQA VerifiedNot measured49.4%Only o3 measured
GeoBenchNot measured74.0%Only o3 measured
LMArena Text: scienceNot measured1429Only o3 measured
LMArena Text: medicine and healthcareNot measured1448Only o3 measured
LMArena Text: legal and governmentNot measured1428Only o3 measured
LMArena Text: business and financeNot measured1393Only o3 measured
Neither model has a result on the other 3 boards here
Web designLike-for-likePublic boards, shown as published, kept out of the index50
Web design benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
Design Arena: websites11621036GPT-5.1-Codex
Design Arena: UI components12371016GPT-5.1-Codex
Design Arena: game dev11381034GPT-5.1-Codex
Design Arena: data viz12131200GPT-5.1-Codex
Design Arena: all code categories11531021GPT-5.1-Codex
Neither model has a result on the other 4 boards here
GeneralLike-for-likePublic boards, shown as published, kept out of the index02
General benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
SAGE (Vals AI)Not measured41.8%Only o3 measured
MedScribe (Vals AI)Not measured76.7%Only o3 measured
IFBench70.0%71.4%o3
Long context reasoning (AA-LCR)69.3%74.7%o3
DTBenchNot measured84.8%Only o3 measured
LMCANot measured39.7%Only o3 measured
Fiction.LiveBenchNot measured88.9%Only o3 measured
Creative writing (Lech Mazur)Not measured83.9%Only o3 measured
CL-benchNot measured17.8%Only o3 measured
LMArena TextNot measured1410Only o3 measured
LMArena Text: instruction followingNot measured1368Only o3 measured
LMArena Text: creative writingNot measured1359Only o3 measured
LMArena VisionNot measured1214Only o3 measured
LMArena Text: EnglishNot measured1417Only o3 measured
LMArena Text: non-EnglishNot measured1401Only o3 measured
LMArena Text: ChineseNot measured1437Only o3 measured
LMArena Text: GermanNot measured1420Only o3 measured
LMArena Text: JapaneseNot measured1403Only o3 measured
LMArena Text: KoreanNot measured1370Only o3 measured
LMArena Text: FrenchNot measured1430Only o3 measured
LMArena Text: SpanishNot measured1395Only o3 measured
LMArena Text: RussianNot measured1406Only o3 measured
LMArena Text: PolishNot measured1438Only o3 measured
LMArena Text: multi-turnNot measured1405Only o3 measured
LMArena Text: longer queriesNot measured1372Only o3 measured
LMArena Text: writing and languageNot measured1372Only o3 measured
LMArena Text: entertainment and mediaNot measured1373Only o3 measured
LMArena Vision: EnglishNot measured1221Only o3 measured
LMArena Vision: ChineseNot measured1237Only o3 measured
LMArena Vision: reading textNot measured1218Only o3 measured
LMArena Vision: humorNot measured1222Only o3 measured
LMArena Vision: captioningNot measured1210Only o3 measured
LMArena Vision: recognizing thingsNot measured1234Only o3 measured
LMArena Vision: creative writingNot measured1201Only o3 measured
Neither model has a result on the other 12 boards here
Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared
Image generation benchmarks for GPT-5.1-Codex and o3
BenchmarkGPT-5.1-Codexo3Leader
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-5.1-Codex$0.0063Fits in one request
o3$0.0060Fits in one request

o3 costs less

Repository review

50K input + 3K output tokens

GPT-5.1-Codex$0.092Fits in one request
o3$0.124Fits in one request

GPT-5.1-Codex costs less

Agent loop

200K input + 10K output tokens

GPT-5.1-Codex$0.350Fits in one request
o3$0.480Exceeds the context window

GPT-5.1-Codex 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-5.1-Codex and o3
SpecificationOpenAI GPT-5.1-CodexOpenAI o3
MakerOpenAIOpenAI
WeightsNo public weights listedNo public weights listed
ReleasedNovember 13, 2025April 16, 2025
Context window400K200K
Input $/Mtok$1.25$2.00
Output $/Mtok$10.00$8.00
Coding index50.570.7
Independent measurements behind it22
Cost per solved task$0.892$0.571
SourceOpenRouter listingOpenRouter listing

Questions

Is GPT-5.1-Codex better than o3 for coding?

Pick o3 for coding: it scores 70.7 on the Vibe Coding Index against 50.5 for GPT-5.1-Codex. Pick GPT-5.1-Codex when the context window is larger, 400K against 200K tokens, or when what matters is SWE-bench Verified or LiveCodeBench (Vals AI), where it leads.

Which is cheaper, GPT-5.1-Codex or o3?

GPT-5.1-Codex costs $1.25 per million input tokens and $10.00 per million output tokens; o3 costs $2.00 and $8.00. Per solved SWE-bench Verified task, GPT-5.1-Codex costs $0.892 and o3 $0.571.

Which has the bigger context window, GPT-5.1-Codex or o3?

GPT-5.1-Codex, with 400K tokens against 200K.

How many benchmarks is the GPT-5.1-Codex vs o3 comparison based on?

19 benchmarks have a result for both models as of October 21, 2026. GPT-5.1-Codex's coding index rests on 2 independent benchmarks and o3's on 2. Where only one model has a result, the page says so instead of naming a winner.

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<p style="font:13px/1.4 sans-serif;margin:6px 0 0">Source: <a href="https://llmbenchmark.ai/compare/gpt-5-1-codex-vs-o3">LLMBenchmark.ai, GPT-5.1-Codex vs o3</a></p>