Model comparison
GPT-5.1-Codex vs Step 3.5 Flash
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 38.6 on the Noometry Index.
Last verified . 0 shared benchmarks.
StepFunSummary
- The widest gap is in math, where Step 3.5 Flash leads 42.6 to 30.3.
- Step 3.5 Flash 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 256K.
- Step 3.5 Flash has downloadable open weights; the other is API-only.
Side by side
| GPT-5.1-Codex | Step 3.5 Flash | |
|---|---|---|
| Provider | OpenAI | StepFun |
| Noometry Index | 38.6 | 42.3 |
| Released | 2025-11-12 | 2026-01-29 |
| Weights | Proprietary | Open |
| Context window | 400K | 256K |
| Max output | 128K | 256K |
| Input $ / M tokens | $1.25 | $0.10 |
| Output $ / M tokens | $10 | $0.30 |
| Results tracked | 6 | 19 |
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Category by category
Coding Too close to call
GPT-5.1-Codex: 41.9 (#116), Step 3.5 Flash: 42.4 (#105)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1337 | — |
| LMArena Coding | — | 1436 |
| ALE-Bench | 1,245 | — |
Agentic & Tool Use Not comparable
GPT-5.1-Codex: 38.0 (#33), Step 3.5 Flash: —
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| METR Time Horizons | 70.8% | — |
Reasoning Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 22.2 (#202)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| NYT Connections (extended) | — | 28.4% |
| LMArena Hard Prompts | — | 1411 |
Math Step 3.5 Flash leads
GPT-5.1-Codex: 30.3 (#235), Step 3.5 Flash: 42.6 (#84)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| MathArena Final-Answer Competitions | — | 66.8% |
| ProofBench | 9% | — |
| LMArena Math | — | 1408 |
Knowledge Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 39.6 (#132)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| LMArena Expert | — | 1421 |
Multilingual Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 50.5 (#119)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | — | 1385 |
| LMArena Chinese | — | 1447 |
| LMArena French | — | 1421 |
| LMArena German | — | 1405 |
| LMArena Japanese | — | 1354 |
| LMArena Korean | — | 1352 |
| LMArena Russian | — | 1385 |
| LMArena Spanish | — | 1419 |
Instruction Following Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 73.1 (#124)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | — | 1385 |
Long Context Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 42.8 (#117)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | — | 1402 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, Step 3.5 Flash: 58.8 (#113)
| Benchmark | GPT-5.1-Codex | Step 3.5 Flash |
|---|---|---|
| LMArena Text | — | 1403 |
| LMArena Creative Writing | — | 1357 |
| LMArena Multi-Turn | — | 1405 |
Frequently asked questions
Is GPT-5.1-Codex better than Step 3.5 Flash?
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 38.6 on the Noometry Index.
Which is cheaper, GPT-5.1-Codex or Step 3.5 Flash?
Step 3.5 Flash 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 GPT-5.1-Codex or Step 3.5 Flash 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?
GPT-5.1-Codex does, with 400K tokens against 256K.
How many benchmarks do GPT-5.1-Codex and Step 3.5 Flash share?
0 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Step 3.5 Flash has 19.