GPT-5.1 vs GPT-5.3 Codex
GPT-5.3 Codex comes out ahead, 64 to 60 on our weighted score, though GPT-5.1 is 29% cheaper per token.
OpenAIGPT-5.1
60/100- ECI149.7
- Price$1.25 / $10.00
- Context400K
- Our pickOpenAI
GPT-5.3 Codex
64/100- ECI156.8
- Price$1.75 / $14.00
- Context400K
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Make it a three-way comparison.
GPT-5.3 Codex is our pick
GPT-5.3 Codex is the better all-round choice, scoring 64/100 against GPT-5.1 (60). It leads on capability and inputs & features. GPT-5.1 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
- CapabilityGPT-5.3 CodexCapabilities Index (ECI): GPT-5.3 Codex 156.8 · GPT-5.1 149.7
- Lowest priceGPT-5.1GPT-5.1 $3.44 · GPT-5.3 Codex $4.81 per 1M tokens (3:1 blend)
- Longest contextAbout the sameGPT-5.1 400,000 · GPT-5.3 Codex 400,000 tokens
- Widest inputsGPT-5.3 CodexGPT-5.1: Text, Images · GPT-5.3 Codex: Text, Images, PDFs
- Self-hostingNo open weightsBoth are available only through APIs
| Measure | Weight | GPT-5.1 | GPT-5.3 Codex |
|---|---|---|---|
| CapabilityCapabilities Index (ECI) | 50% | 78 | 87 |
| Price | 25% | 24 | 18 |
| Inputs & features | 15% | 70 | 80 |
| Context window | 10% | 44 | 44 |
| Overall | 100% | 60/100 | 64/100 |
Every spec in one table
Highlighted cells lead their row. Dashes mean the data is not published.
| Specification | GPT-5.1OpenAI | GPT-5.3 CodexOpenAI |
|---|---|---|
| Capability | ||
| Capabilities Index (ECI) | 149.7 | 156.8 (best) |
| ECI rank | #52 of 148 | #18 of 148 (best) |
| GPQA DiamondGraduate-level science questions | 87.6% | — |
| OTIS Mock AIME 2024–2025Competition mathematics | 88.6% | — |
| SWE-bench VerifiedFixing real GitHub issues | 68.0% | 74.8% (best) |
| SimpleQA VerifiedShort factual questions | 48.0% | — |
| Price per million tokens | ||
| Input | $1.25 (best) | $1.75 |
| Output | $10.00 (best) | $14.00 |
| Cached input | $0.125 (best) | $0.175 |
| Blended (3:1) | $3.44 (best) | $4.81 |
| Long-context rate | Same rate | Same rate |
| Price source | Official OpenAI API | Official OpenAI API |
| Limits | ||
| Context window | 400,000 tokens | 400,000 tokens |
| Max output | 128,000 tokens | 128,000 tokens |
| Inputs and features | ||
| Text | Yes | Yes |
| Images | Yes | Yes |
| PDFs | No | Yes |
| Audio | No | No |
| Video | No | No |
| Reasoning | Yeslow · medium · high | Yeslow · medium · high · xhigh |
| Tool calling | Yes | Yes |
| Structured output | Yes | Yes |
| Availability | ||
| Weights | Proprietary | Proprietary |
| API model ID | gpt-5.1 | gpt-5.3-codex |
| API providers | 21 (best) | 19 |
| Released | Nov 13, 2025 | Feb 5, 2026 |
| Knowledge cutoff | Sep 30, 2024 | Aug 31, 2025 |
What would a month cost?
Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.
- GPT-5.1$32.50
- GPT-5.3 Codex$45.50
Which should you choose?
Which is better: GPT-5.1 or GPT-5.3 Codex?
GPT-5.3 Codex is the better all-round choice, scoring 64/100 against GPT-5.1 (60). It leads on capability and inputs & features. GPT-5.1 wins on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.
Which is cheaper, GPT-5.1 or GPT-5.3 Codex?
GPT-5.1 is cheaper at $1.25 input / $10.00 output per million tokens (official OpenAI API price). GPT-5.3 Codex costs $1.75 input / $14.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $3.44 per million tokens for GPT-5.1 versus $4.81 for GPT-5.3 Codex (1.4× as much).
Which scores higher on benchmarks?
GPT-5.3 Codex scores higher on the Capabilities Index (ECI): GPT-5.3 Codex 156.8 (#18 of 148) and GPT-5.1 149.7 (#52 of 148). Their confidence ranges do not overlap (153.5–160.8 vs 148.3–151.1), so the gap is a real one. On individual benchmarks: SWE-bench Verified — GPT-5.3 Codex 74.8%, GPT-5.1 68.0%.
Which is better for coding?
GPT-5.3 Codex resolves more real GitHub issues on SWE-bench Verified: GPT-5.3 Codex 74.8% and GPT-5.1 68.0%. Both support tool calling for agent workflows.
Which has the bigger context window?
GPT-5.1 and GPT-5.3 Codex share the same 400,000-token context window. Maximum output per response: GPT-5.1 up to 128,000, GPT-5.3 Codex up to 128,000 tokens.
Which can read images, PDFs, audio or video?
GPT-5.1 accepts text and images; GPT-5.3 Codex accepts text, images and PDFs. GPT-5.3 Codex handles the widest range of inputs.
Are any of these open source?
No. GPT-5.1 and GPT-5.3 Codex are proprietary and only available through APIs and apps.
Which is newer?
GPT-5.3 Codex is the newest, released Feb 5, 2026. GPT-5.1 came out Nov 13, 2025. Knowledge cutoff: GPT-5.1 Sep 30, 2024, GPT-5.3 Codex Aug 31, 2025.
How do you decide the winner?
Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.
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