Model comparison
GPT-5.1-Codex vs GPT-5-Codex
GPT-5.1-Codex and GPT-5-Codex score almost the same on the Noometry Index (38.6 vs 37.9), so choose on price, context window or the category you care about most.
Last verified . 1 shared benchmarks.
Summary
- They share 1 benchmark with published results for both. GPT-5.1-Codex scores higher in 1 category and GPT-5-Codex in 1 category; one gap is clear of the uncertainty.
- The widest gap is in agentic & tool use, where GPT-5.1-Codex leads 38.0 to 31.0.
- The biggest single-benchmark swing is Terminal-Bench: 60.4% for GPT-5.1-Codex and 44.3% for GPT-5-Codex.
- Both cost about the same: $1.25 input and $10 output per million tokens.
Side by side
| GPT-5.1-Codex | GPT-5-Codex | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 38.6 | 37.9 |
| Released | 2025-11-12 | 2025-09-15 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 400K |
| Max output | 128K | 128K |
| Input $ / M tokens | $1.25 | $1.25 |
| Output $ / M tokens | $10 | $10 |
| Results tracked | 6 | 3 |
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Category by category
Coding Too close to call
GPT-5.1-Codex: 41.9 (#116), GPT-5-Codex: 42.4 (#103)
| Benchmark | GPT-5.1-Codex | GPT-5-Codex |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| WeirdML | — | 54.5% |
| ALE-Bench | 1,245 | — |
Agentic & Tool Use GPT-5.1-Codex leads
GPT-5.1-Codex: 38.0 (#33), GPT-5-Codex: 31.0 (#72)
| Benchmark | GPT-5.1-Codex | GPT-5-Codex |
|---|---|---|
| Terminal-Bench | 60.4% | 44.3% |
| METR Time Horizons | 70.8% | — |
Reasoning Not comparable
GPT-5.1-Codex: —, GPT-5-Codex: 30.9 (#83)
| Benchmark | GPT-5.1-Codex | GPT-5-Codex |
|---|---|---|
| Kagi LLM Benchmark | — | 70.3% |
Math Not comparable
GPT-5.1-Codex: 30.3 (#235), GPT-5-Codex: —
| Benchmark | GPT-5.1-Codex | GPT-5-Codex |
|---|---|---|
| ProofBench | 9% | — |
Frequently asked questions
Is GPT-5.1-Codex better than GPT-5-Codex?
GPT-5.1-Codex and GPT-5-Codex score almost the same on the Noometry Index (38.6 vs 37.9), so choose on price, context window or the category you care about most.
Which is cheaper, GPT-5.1-Codex or GPT-5-Codex?
GPT-5-Codex is cheaper. It lists at $1.25 per million input tokens and $10 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.
Is GPT-5.1-Codex or GPT-5-Codex better for coding?
They score almost the same on coding (41.9 vs 42.4); test both on your own repository before choosing.
Which has the bigger context window?
Both accept 400K tokens.
How many benchmarks do GPT-5.1-Codex and GPT-5-Codex share?
1 benchmark has published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and GPT-5-Codex has 3.