# GPT-5.1 vs Step 3.5 Flash

> GPT-5.1 is the stronger model overall, scoring 49.0 to 42.3 on the Noometry Index. Step 3.5 Flash costs 23× less per token, which makes it the better buy when GPT-5.1's lead doesn't matter for your workload.

- Canonical page: https://noometry.com/compare/gpt-5-1-vs-step-3-5-flash
- Last updated: 2026-10-10
- Shared benchmarks: 17

## Summary

- They share 17 benchmarks with published results for both. GPT-5.1 scores higher in 8 categories and Step 3.5 Flash in 0 categories; 8 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where GPT-5.1 leads 39.8 to 22.2.
- Step 3.5 Flash is cheaper at $0.10 / $0.30 per million input/output tokens, against $1.25 / $10 for GPT-5.1.
- GPT-5.1 accepts more context: 400K tokens versus 256K.
- Step 3.5 Flash has downloadable open weights; the other is API-only.

## Snapshot

| | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| Provider | OpenAI | StepFun |
| Noometry Index | 49.0 | 42.3 |
| Rank | 53 | 116 |
| Context | 400K | 256K |
| Input $/M | $1.25 | $0.10 |
| Output $/M | $10 | $0.30 |
| Weights | Proprietary | Open |

## Coding

- GPT-5.1: 46.4 (#66)
- Step 3.5 Flash: 42.4 (#105)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Coding | 1454 | 1436 |
| SWE-bench Verified | 68% | — |
| SWE-bench Verified (bash only) | 66% | — |
| LMArena WebDev | 1395 | — |
| SciCode | 43.3% | — |
| GSO | 13.7% | — |
| WeirdML | 60.8% | — |
| LiveBench Coding | 72.5% | — |
| ALE-Bench | 1,192 | — |

## Agentic & Tool Use

- GPT-5.1: 32.7 (#60)
- Step 3.5 Flash: —

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| Terminal-Bench | 47.6% | — |
| DeepResearch Bench | 42.8% | — |
| LMArena Search | 1199 | — |
| Vending-Bench 2 | 1,473 | — |

## Reasoning

- GPT-5.1: 39.8 (#58)
- Step 3.5 Flash: 22.2 (#202)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Hard Prompts | 1457 | 1411 |
| ARC-AGI-2 | 17.6% | — |
| SimpleBench | 53.2% | — |
| NYT Connections (extended) | — | 28.4% |
| ARC-AGI-1 | 72.8% | — |
| CritPt | 4.9% | — |
| Chess Puzzles | 32% | — |
| EnigmaEval | 11.2% | — |
| LiveBench Reasoning | 95.8% | — |
| Mystery Game Puzzles | 19% | — |
| DTBench | 90.1% | — |
| LiveBench Data Analysis | 72.1% | — |
| LMCA | 43.9% | — |
| Epoch Capabilities Index | 149.64 | — |
| ForecastBench | 58.1 | — |
| LiveBench | 78.8% | — |

## Math

- GPT-5.1: 52.2 (#51)
- Step 3.5 Flash: 42.6 (#84)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Math | 1447 | 1408 |
| MathArena Final-Answer Competitions | — | 66.8% |
| OTIS Mock AIME 2024-2025 | 88.6% | — |
| Omni-MATH | 46.4% | — |
| LiveBench Math | 94.5% | — |
| FrontierMath (Feb 2025 set) | 31% | — |
| FrontierMath Tier 4 (v1) | 12.5% | — |

## Knowledge

- GPT-5.1: 50.6 (#71)
- Step 3.5 Flash: 39.6 (#132)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Expert | 1470 | 1421 |
| GPQA Diamond | 87.6% | — |
| Humanity's Last Exam | 23.7% | — |
| SimpleQA Verified | 48% | — |
| MMLU-Pro | 57.9% | — |
| Vectara Hallucination Rate | 10.9% | — |
| GPQA (HELM) | 44.2% | — |

## Multimodal

- GPT-5.1: 44.8 (#19)
- Step 3.5 Flash: —

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Vision | 1250 | — |
| VPCT | 58.7% | — |
| LMArena Document | 1403 | — |

## Multilingual

- GPT-5.1: 53.8 (#56)
- Step 3.5 Flash: 50.5 (#119)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | 1431 | 1385 |
| LMArena Chinese | 1495 | 1447 |
| LMArena French | 1450 | 1421 |
| LMArena German | 1438 | 1405 |
| LMArena Japanese | 1453 | 1354 |
| LMArena Korean | 1401 | 1352 |
| LMArena Russian | 1435 | 1385 |
| LMArena Spanish | 1433 | 1419 |

## Instruction Following

- GPT-5.1: 83.9 (#1)
- Step 3.5 Flash: 73.1 (#124)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | 1443 | 1385 |
| LiveBench Instruction Following | 93.3% | — |
| IFEval | 93.5% | — |

## Long Context

- GPT-5.1: 47.6 (#14)
- Step 3.5 Flash: 42.8 (#117)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | 1447 | 1402 |
| CL-bench | 23.7% | — |
| CL-bench Life | 17.3% | — |

## Writing & Preference

- GPT-5.1: 64.5 (#55)
- Step 3.5 Flash: 58.8 (#113)

| Benchmark | GPT-5.1 | Step 3.5 Flash |
|---|---|---|
| LMArena Text | 1443 | 1403 |
| LMArena Creative Writing | 1427 | 1357 |
| LMArena Multi-Turn | 1450 | 1405 |
| WildBench | 86.3% | — |
| LiveBench Language | 80.2% | — |

## FAQ

### Is GPT-5.1 better than Step 3.5 Flash?

GPT-5.1 is the stronger model overall, scoring 49.0 to 42.3 on the Noometry Index. Step 3.5 Flash costs 23× less per token, which makes it the better buy when GPT-5.1's lead doesn't matter for your workload.

### Which is cheaper, GPT-5.1 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 lists at $1.25 and $10.

### Is GPT-5.1 or Step 3.5 Flash better for coding?

GPT-5.1 scores higher on coding benchmarks: 46.4 versus 42.4 in the Noometry coding category.

### Which has the bigger context window?

GPT-5.1 does, with 400K tokens against 256K.

### How many benchmarks do GPT-5.1 and Step 3.5 Flash share?

17 benchmarks have published results for both models. GPT-5.1 has 63 scored results on Noometry and Step 3.5 Flash has 19.