Model comparison
Devstral Small 2505 vs GPT-5.1-Codex
GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 34.3 on the Noometry Index. Devstral Small 2505 costs 23× less per token, which makes it the better buy when GPT-5.1-Codex's lead doesn't matter for your workload.
Last verified . 1 shared benchmarks.
Mistral AISummary
- They share 1 benchmark with published results for both. Devstral Small 2505 scores higher in 0 categories and GPT-5.1-Codex in 1 category; one gap is clear of the uncertainty.
- The biggest single-benchmark swing is SWE-bench Verified (bash only): 56.4% for Devstral Small 2505 and 66% for GPT-5.1-Codex.
- Devstral Small 2505 is cheaper at $0.10 / $0.30 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- GPT-5.1-Codex accepts more context: 400K tokens versus 128K.
- Devstral Small 2505 has downloadable open weights; the other is API-only.
Side by side
| Devstral Small 2505 | GPT-5.1-Codex | |
|---|---|---|
| Provider | Mistral AI | OpenAI |
| Noometry Index | 34.3 | 38.6 |
| Released | 2025-05-07 | 2025-11-12 |
| Weights | Open | Proprietary |
| Context window | 128K | 400K |
| Max output | 128K | 128K |
| Input $ / M tokens | $0.10 | $1.25 |
| Output $ / M tokens | $0.30 | $10 |
| Results tracked | 4 | 6 |
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Category by category
Coding GPT-5.1-Codex leads
Devstral Small 2505: 38.9 (#166), GPT-5.1-Codex: 41.9 (#116)
| Benchmark | Devstral Small 2505 | GPT-5.1-Codex |
|---|---|---|
| SWE-bench Verified (bash only) | 56.4% | 66% |
| LMArena WebDev | — | 1337 |
| SciCode | 28.8% | — |
| ALE-Bench | — | 1,245 |
Agentic & Tool Use Not comparable
Devstral Small 2505: —, GPT-5.1-Codex: 38.0 (#33)
| Benchmark | Devstral Small 2505 | GPT-5.1-Codex |
|---|---|---|
| Terminal-Bench | — | 60.4% |
| METR Time Horizons | — | 70.8% |
Reasoning Not comparable
Devstral Small 2505: 19.7 (#252), GPT-5.1-Codex: —
| Benchmark | Devstral Small 2505 | GPT-5.1-Codex |
|---|---|---|
| Kagi LLM Benchmark | 37.7% | — |
| CritPt | 0% | — |
Math Not comparable
Devstral Small 2505: —, GPT-5.1-Codex: 30.3 (#235)
| Benchmark | Devstral Small 2505 | GPT-5.1-Codex |
|---|---|---|
| ProofBench | — | 9% |
Frequently asked questions
Is Devstral Small 2505 better than GPT-5.1-Codex?
GPT-5.1-Codex is the stronger model overall, scoring 38.6 to 34.3 on the Noometry Index. Devstral Small 2505 costs 23× 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, Devstral Small 2505 or GPT-5.1-Codex?
Devstral Small 2505 is cheaper. It lists at $0.10 per million input tokens and $0.30 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.
Is Devstral Small 2505 or GPT-5.1-Codex better for coding?
GPT-5.1-Codex scores higher on coding benchmarks: 41.9 versus 38.9 in the Noometry coding category.
Which has the bigger context window?
GPT-5.1-Codex does, with 400K tokens against 128K.
How many benchmarks do Devstral Small 2505 and GPT-5.1-Codex share?
1 benchmark has published results for both models. Devstral Small 2505 has 4 scored results on Noometry and GPT-5.1-Codex has 6.