Model comparison
GPT-5.1-Codex vs GPT-5 Nano
GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 33.5 on the Noometry Index. GPT-5 Nano costs 25× less per token, which makes it the better buy when GPT-5.1-Codex's lead doesn't matter for your workload.
Last verified . 4 shared benchmarks.
Summary
- They share 4 benchmarks with published results for both. GPT-5.1-Codex scores higher in 3 categories and GPT-5 Nano in 0 categories; 2 gaps are clear of the uncertainty.
- The widest gap is in agentic & tool use, where GPT-5.1-Codex leads 38.0 to 25.8.
- The biggest single-benchmark swing is Terminal-Bench: 60.4% for GPT-5.1-Codex and 21.8% for GPT-5 Nano.
- GPT-5 Nano is cheaper at $0.05 / $0.40 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
Side by side
| GPT-5.1-Codex | GPT-5 Nano | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.6 | 33.5 |
| Released | 2025-11-12 | 2025-08-07 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 400K |
| Max output | 128K | 128K |
| Input $ / M tokens | $1.25 | $0.05 |
| Output $ / M tokens | $10 | $0.40 |
| Results tracked | 6 | 49 |
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Category by category
Coding GPT-5.1-Codex leads
GPT-5.1-Codex: 41.9 (#116), GPT-5 Nano: 33.6 (#254)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | 34.8% |
| ALE-Bench | 1,245 | 718.67 |
| LMArena WebDev | 1337 | — |
| WeirdML | — | 38.1% |
| LMArena Coding | — | 1351 |
Agentic & Tool Use GPT-5.1-Codex leads
GPT-5.1-Codex: 38.0 (#33), GPT-5 Nano: 25.8 (#106)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| Terminal-Bench | 60.4% | 21.8% |
| Berkeley Function Calling Leaderboard | — | 51.5% |
| METR Time Horizons | 70.8% | — |
Reasoning Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 16.3 (#306)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| ARC-AGI-2 | — | 2.6% |
| Kagi LLM Benchmark | — | 62.2% |
| ARC-AGI-1 | — | 20.7% |
| Chess Puzzles | — | 27% |
| LMArena Hard Prompts | — | 1328 |
| Mystery Game Puzzles | — | 9% |
| DTBench | — | 62.7% |
| LMCA | — | 7.9% |
| Epoch Capabilities Index | — | 139.38 |
| ForecastBench | — | 59.1 |
Math Too close to call
GPT-5.1-Codex: 30.3 (#235), GPT-5 Nano: 29.4 (#241)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| ProofBench | 9% | 12% |
| FrontierMath (Tiers 1-3) | — | 20% |
| FrontierMath Tier 4 | — | 2.4% |
| OTIS Mock AIME 2024-2025 | — | 81.1% |
| Omni-MATH | — | 54.6% |
| LMArena Math | — | 1317 |
| MATH Level 5 | — | 95.2% |
| FrontierMath (Feb 2025 set) | — | 8.3% |
| FrontierMath Tier 4 (v1) | — | 2.1% |
Knowledge Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 35.9 (#178)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| GPQA Diamond | — | 69.4% |
| SimpleQA Verified | — | 11.7% |
| MMLU-Pro | — | 77.8% |
| Vectara Hallucination Rate | — | 10.5% |
| GPQA (HELM) | — | 67.9% |
| LMArena Expert | — | 1321 |
Multimodal Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 31.3 (#108)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| LMArena Vision | — | 1159 |
| VPCT | — | 37.2% |
Multilingual Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 45.3 (#172)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| LMArena Non-English | — | 1313 |
| LMArena Chinese | — | 1356 |
| LMArena German | — | 1327 |
| LMArena Japanese | — | 1226 |
| LMArena Korean | — | 1269 |
| LMArena Russian | — | 1296 |
| LMArena Spanish | — | 1360 |
Instruction Following Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 75.0 (#79)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| IFEval | — | 93.2% |
| LMArena Instruction Following | — | 1306 |
Long Context Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 31.3 (#281)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| Fiction.LiveBench | — | 44.4% |
| LMArena Longer Query | — | 1312 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, GPT-5 Nano: 39.1 (#249)
| Benchmark | GPT-5.1-Codex | GPT-5 Nano |
|---|---|---|
| LMArena Text | — | 1320 |
| LMArena Creative Writing | — | 1249 |
| EQ-Bench Creative Writing | — | 705 |
| WildBench | — | 80.6% |
| LMArena Multi-Turn | — | 1311 |
Frequently asked questions
Is GPT-5.1-Codex better than GPT-5 Nano?
GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 33.5 on the Noometry Index. GPT-5 Nano costs 25× less per token, which makes it the better buy when GPT-5.1-Codex's lead doesn't matter for your workload.
Which is cheaper, GPT-5.1-Codex or GPT-5 Nano?
GPT-5 Nano is cheaper. It lists at $0.05 per million input tokens and $0.40 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.
Is GPT-5.1-Codex or GPT-5 Nano better for coding?
GPT-5.1-Codex scores higher on coding benchmarks: 41.9 versus 33.6 in the Noometry coding category.
Which has the bigger context window?
Both accept 400K tokens.
How many benchmarks do GPT-5.1-Codex and GPT-5 Nano share?
4 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5 Nano has 49.