Model comparison
Grok 4 Fast vs Step 3.5 Flash
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 39.4 on the Noometry Index.
Last verified . 17 shared benchmarks.
StepFunSummary
- They share 17 benchmarks with published results for both. Grok 4 Fast scores higher in 5 categories and Step 3.5 Flash in 3 categories; 5 gaps are clear of the uncertainty.
- The widest gap is in long context, where Grok 4 Fast leads 63.2 to 42.8.
- Step 3.5 Flash has downloadable open weights; the other is API-only.
Side by side
| Grok 4 Fast | Step 3.5 Flash | |
|---|---|---|
| Provider | xAI | StepFun |
| Noometry Index | 39.4 | 42.3 |
| Released | 2025-09-19 | 2026-01-29 |
| Weights | Proprietary | Open |
| Context window | — | 256K |
| Max output | — | 256K |
| Input $ / M tokens | — | $0.10 |
| Output $ / M tokens | — | $0.30 |
| Results tracked | 30 | 19 |
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Category by category
Coding Step 3.5 Flash leads
Grok 4 Fast: 32.5 (#271), Step 3.5 Flash: 42.4 (#105)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Coding | 1429 | 1436 |
| LMArena WebDev | 1159 | — |
| WeirdML | 42.9% | — |
Agentic & Tool Use Not comparable
Grok 4 Fast: 29.5 (#86), Step 3.5 Flash: —
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| τ²-bench Banking | 15.7% | — |
| Cybench | 30% | — |
| LMArena Search | 1171 | — |
Reasoning Too close to call
Grok 4 Fast: 22.2 (#201), Step 3.5 Flash: 22.2 (#202)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Hard Prompts | 1412 | 1411 |
| ARC-AGI-2 | 5.3% | — |
| Kagi LLM Benchmark | 66.1% | — |
| NYT Connections (extended) | — | 28.4% |
| ARC-AGI-1 | 48.5% | — |
| DTBench | 82.7% | — |
| Epoch Capabilities Index | 144.2 | — |
| ForecastBench | 60.5 | — |
Math Step 3.5 Flash leads
Grok 4 Fast: 38.9 (#123), Step 3.5 Flash: 42.6 (#84)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Math | 1419 | 1408 |
| MathArena Final-Answer Competitions | — | 66.8% |
Knowledge Step 3.5 Flash leads
Grok 4 Fast: 32.0 (#214), Step 3.5 Flash: 39.6 (#132)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Expert | 1411 | 1421 |
| Vectara Hallucination Rate | 19.7% | — |
Multilingual Too close to call
Grok 4 Fast: 51.3 (#111), Step 3.5 Flash: 50.5 (#119)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Non-English | 1396 | 1385 |
| LMArena Chinese | 1457 | 1447 |
| LMArena French | 1431 | 1421 |
| LMArena German | 1383 | 1405 |
| LMArena Japanese | 1352 | 1354 |
| LMArena Korean | 1357 | 1352 |
| LMArena Russian | 1389 | 1385 |
| LMArena Spanish | 1415 | 1419 |
Instruction Following Too close to call
Grok 4 Fast: 73.2 (#121), Step 3.5 Flash: 73.1 (#124)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Instruction Following | 1387 | 1385 |
Long Context Grok 4 Fast leads
Grok 4 Fast: 63.2 (#3), Step 3.5 Flash: 42.8 (#117)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Longer Query | 1415 | 1402 |
| Fiction.LiveBench | 94.4% | — |
Writing & Preference Grok 4 Fast leads
Grok 4 Fast: 60.0 (#102), Step 3.5 Flash: 58.8 (#113)
| Benchmark | Grok 4 Fast | Step 3.5 Flash |
|---|---|---|
| LMArena Text | 1407 | 1403 |
| LMArena Creative Writing | 1387 | 1357 |
| LMArena Multi-Turn | 1414 | 1405 |
Frequently asked questions
Is Grok 4 Fast better than Step 3.5 Flash?
Step 3.5 Flash is the stronger model overall, scoring 42.3 to 39.4 on the Noometry Index.
Is Grok 4 Fast or Step 3.5 Flash better for coding?
Step 3.5 Flash scores higher on coding benchmarks: 42.4 versus 32.5 in the Noometry coding category.
How many benchmarks do Grok 4 Fast and Step 3.5 Flash share?
17 benchmarks have published results for both models. Grok 4 Fast has 30 scored results on Noometry and Step 3.5 Flash has 19.