# Claude Sonnet 4.5 vs Step 3.5 Flash

> Claude Sonnet 4.5 is the stronger model overall, scoring 44.1 to 42.3 on the Noometry Index. Step 3.5 Flash costs 40× less per token, which makes it the better buy when Claude Sonnet 4.5's lead doesn't matter for your workload.

- Canonical page: https://noometry.com/compare/claude-sonnet-4-5-vs-step-3-5-flash
- Last updated: 2026-10-12
- Shared benchmarks: 18

## Summary

- They share 18 benchmarks with published results for both. Claude Sonnet 4.5 scores higher in 7 categories and Step 3.5 Flash in 1 category; 8 gaps are clear of the uncertainty.
- The widest gap is in math, where Step 3.5 Flash leads 42.6 to 32.3.
- The biggest single-benchmark swing is NYT Connections (extended): 37.3% for Claude Sonnet 4.5 and 28.4% for Step 3.5 Flash.
- Step 3.5 Flash is cheaper at $0.10 / $0.30 per million input/output tokens, against $3 / $15 for Claude Sonnet 4.5.
- Step 3.5 Flash accepts more context: 256K tokens versus 200K.
- Step 3.5 Flash has downloadable open weights; the other is API-only.

## Snapshot

| | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| Provider | Anthropic | StepFun |
| Noometry Index | 44.1 | 42.3 |
| Rank | 81 | 116 |
| Context | 200K | 256K |
| Input $/M | $3 | $0.10 |
| Output $/M | $15 | $0.30 |
| Weights | Proprietary | Open |

## Coding

- Claude Sonnet 4.5: 47.3 (#61)
- Step 3.5 Flash: 42.4 (#105)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Coding | 1489 | 1436 |
| SWE-bench Verified | 71.3% | — |
| SWE-bench Verified (bash only) | 71.4% | — |
| LMArena WebDev | 1393 | — |
| SWE-bench Multilingual | 67% | — |
| SciCode | 44.7% | — |
| GSO | 14.7% | — |
| WeirdML | 47.7% | — |
| ALE-Bench | 796.15 | — |
| AlgoTune | 1.52 | — |

## Agentic & Tool Use

- Claude Sonnet 4.5: 38.3 (#32)
- Step 3.5 Flash: —

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| Terminal-Bench | 46.5% | — |
| Berkeley Function Calling Leaderboard | 73.2% | — |
| GDPval | 42.5% | — |
| Remote Labor Index | 2.1% | — |
| τ²-bench Airline | 72% | — |
| τ²-bench Banking | 25.3% | — |
| τ²-bench Retail | 72.4% | — |
| τ²-bench Telecom | 84.9% | — |
| Cybench | 60% | — |
| DeepResearch Bench | 52.6% | — |
| OSWorld | 62.9% | — |
| LMArena Search | 1159 | — |
| METR Time Horizons | 67.4% | — |
| Vending-Bench 2 | 3,839 | — |

## Reasoning

- Claude Sonnet 4.5: 26.9 (#125)
- Step 3.5 Flash: 22.2 (#202)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| NYT Connections (extended) | 37.3% | 28.4% |
| LMArena Hard Prompts | 1462 | 1411 |
| ARC-AGI-2 | 13.6% | — |
| SimpleBench | 54.3% | — |
| Kagi LLM Benchmark | 57.9% | — |
| ARC-AGI-1 | 63.7% | — |
| CritPt | 1.1% | — |
| Chess Puzzles | 12% | — |
| EnigmaEval | 6% | — |
| EBR-Bench | 2.4% | — |
| Mystery Game Puzzles | 17% | — |
| DTBench | 83.2% | — |
| LMCA | 38.8% | — |
| Epoch Capabilities Index | 146.84 | — |
| ForecastBench | 61.9 | — |

## Math

- Claude Sonnet 4.5: 32.3 (#216)
- Step 3.5 Flash: 42.6 (#84)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Math | 1449 | 1408 |
| FrontierMath (Tiers 1-3) | 23.9% | — |
| FrontierMath Tier 4 | 2.4% | — |
| MathArena Final-Answer Competitions | — | 66.8% |
| OTIS Mock AIME 2024-2025 | 77.8% | — |
| ProofBench | 19% | — |
| Omni-MATH | 55.3% | — |
| MATH Level 5 | 97.7% | — |
| FrontierMath (Feb 2025 set) | 15.2% | — |
| FrontierMath Tier 4 (v1) | 4.2% | — |

## Knowledge

- Claude Sonnet 4.5: 48.4 (#76)
- Step 3.5 Flash: 39.6 (#132)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Expert | 1482 | 1421 |
| GPQA Diamond | 82.3% | — |
| Humanity's Last Exam | 13.7% | — |
| SimpleQA Verified | 30.7% | — |
| MMLU-Pro | 86.9% | — |
| Vectara Hallucination Rate | 12% | — |
| GPQA (HELM) | 68.6% | — |

## Multimodal

- Claude Sonnet 4.5: 34.8 (#89)
- Step 3.5 Flash: —

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| VPCT | 39.8% | — |
| LMArena Document | 1450 | — |

## Multilingual

- Claude Sonnet 4.5: 53.4 (#69)
- Step 3.5 Flash: 50.5 (#119)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | 1425 | 1385 |
| LMArena Chinese | 1459 | 1447 |
| LMArena French | 1458 | 1421 |
| LMArena German | 1427 | 1405 |
| LMArena Japanese | 1390 | 1354 |
| LMArena Korean | 1403 | 1352 |
| LMArena Russian | 1437 | 1385 |
| LMArena Spanish | 1457 | 1419 |

## Instruction Following

- Claude Sonnet 4.5: 75.0 (#78)
- Step 3.5 Flash: 73.1 (#124)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | 1459 | 1385 |
| IFEval | 85% | — |

## Long Context

- Claude Sonnet 4.5: 45.2 (#46)
- Step 3.5 Flash: 42.8 (#117)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | 1476 | 1402 |

## Writing & Preference

- Claude Sonnet 4.5: 66.5 (#34)
- Step 3.5 Flash: 58.8 (#113)

| Benchmark | Claude Sonnet 4.5 | Step 3.5 Flash |
|---|---|---|
| LMArena Text | 1439 | 1403 |
| LMArena Creative Writing | 1442 | 1357 |
| LMArena Multi-Turn | 1465 | 1405 |
| EQ-Bench Creative Writing | 1678 | — |
| WildBench | 85.4% | — |

## FAQ

### Is Claude Sonnet 4.5 better than Step 3.5 Flash?

Claude Sonnet 4.5 is the stronger model overall, scoring 44.1 to 42.3 on the Noometry Index. Step 3.5 Flash costs 40× less per token, which makes it the better buy when Claude Sonnet 4.5's lead doesn't matter for your workload.

### Which is cheaper, Claude Sonnet 4.5 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; Claude Sonnet 4.5 lists at $3 and $15.

### Is Claude Sonnet 4.5 or Step 3.5 Flash better for coding?

Claude Sonnet 4.5 scores higher on coding benchmarks: 47.3 versus 42.4 in the Noometry coding category.

### Which has the bigger context window?

Step 3.5 Flash does, with 256K tokens against 200K.

### How many benchmarks do Claude Sonnet 4.5 and Step 3.5 Flash share?

18 benchmarks have published results for both models. Claude Sonnet 4.5 has 73 scored results on Noometry and Step 3.5 Flash has 19.