# Grok 4 Fast vs Llama 3.1-405B

> Grok 4 Fast is the stronger model overall, scoring 39.4 to 30.7 on the Noometry Index.

- Canonical page: https://noometry.com/compare/grok-4-fast-vs-llama-3-1-405b
- Last updated: 2026-10-10
- Shared benchmarks: 23

## Summary

- They share 23 benchmarks with published results for both. Grok 4 Fast scores higher in 8 categories and Llama 3.1-405B in 1 category; 8 gaps are clear of the uncertainty.
- The widest gap is in long context, where Grok 4 Fast leads 63.2 to 38.4.
- The biggest single-benchmark swing is Cybench: 30% for Grok 4 Fast and 7.5% for Llama 3.1-405B.
- Llama 3.1-405B has downloadable open weights; the other is API-only.

## Snapshot

| | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| Provider | xAI | Meta |
| Noometry Index | 39.4 | 30.7 |
| Rank | 167 | 288 |
| Context | — | — |
| Input $/M | — | — |
| Output $/M | — | — |
| Weights | Proprietary | Open |

## Coding

- Grok 4 Fast: 32.5 (#271)
- Llama 3.1-405B: 33.1 (#262)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| WeirdML | 42.9% | 21.4% |
| LMArena Coding | 1429 | 1291 |
| LMArena WebDev | 1159 | — |

## Agentic & Tool Use

- Grok 4 Fast: 29.5 (#86)
- Llama 3.1-405B: 21.0 (#140)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| Cybench | 30% | 7.5% |
| TheAgentCompany | — | 7.4% |
| τ²-bench Banking | 15.7% | — |
| LMArena Search | 1171 | — |

## Reasoning

- Grok 4 Fast: 22.2 (#201)
- Llama 3.1-405B: 16.8 (#300)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| Kagi LLM Benchmark | 66.1% | 45% |
| LMArena Hard Prompts | 1412 | 1269 |
| DTBench | 82.7% | 61.4% |
| Epoch Capabilities Index | 144.2 | 128.75 |
| ForecastBench | 60.5 | 59.9 |
| ARC-AGI-2 | 5.3% | — |
| SimpleBench | — | 23% |
| ARC-AGI-1 | 48.5% | — |
| BIG-Bench Hard | — | 82.9% |
| HellaSwag | — | 89.2% |
| PIQA | — | 85.9% |
| WinoGrande | — | 89.2% |

## Math

- Grok 4 Fast: 38.9 (#123)
- Llama 3.1-405B: 18.4 (#290)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Math | 1419 | 1281 |
| OTIS Mock AIME 2024-2025 | — | 9.7% |
| Omni-MATH | — | 24.9% |
| MATH Level 5 | — | 49.8% |

## Knowledge

- Grok 4 Fast: 32.0 (#214)
- Llama 3.1-405B: 30.4 (#227)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Expert | 1411 | 1243 |
| GPQA Diamond | — | 50.9% |
| MMLU-Pro | — | 72.3% |
| Confabulations | — | 17.6% |
| Vectara Hallucination Rate | 19.7% | — |
| GPQA (HELM) | — | 52.2% |
| ARC (AI2) Challenge | — | 95.3% |
| MMLU | — | 84.5% |
| TriviaQA | — | 82.7% |

## Multilingual

- Grok 4 Fast: 51.3 (#111)
- Llama 3.1-405B: 40.7 (#214)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Non-English | 1396 | 1248 |
| LMArena Chinese | 1457 | 1242 |
| LMArena French | 1431 | 1279 |
| LMArena German | 1383 | 1252 |
| LMArena Japanese | 1352 | 1208 |
| LMArena Korean | 1357 | 1184 |
| LMArena Russian | 1389 | 1265 |
| LMArena Spanish | 1415 | 1260 |

## Instruction Following

- Grok 4 Fast: 73.2 (#121)
- Llama 3.1-405B: 65.9 (#214)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Instruction Following | 1387 | 1259 |
| IFEval | — | 81.1% |

## Long Context

- Grok 4 Fast: 63.2 (#3)
- Llama 3.1-405B: 38.4 (#197)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Longer Query | 1415 | 1266 |
| Fiction.LiveBench | 94.4% | — |

## Writing & Preference

- Grok 4 Fast: 60.0 (#102)
- Llama 3.1-405B: 38.9 (#251)

| Benchmark | Grok 4 Fast | Llama 3.1-405B |
|---|---|---|
| LMArena Text | 1407 | 1284 |
| LMArena Creative Writing | 1387 | 1262 |
| LMArena Multi-Turn | 1414 | 1297 |
| EQ-Bench Creative Writing | — | 870 |
| WildBench | — | 78.3% |

## FAQ

### Is Grok 4 Fast better than Llama 3.1-405B?

Grok 4 Fast is the stronger model overall, scoring 39.4 to 30.7 on the Noometry Index.

### Is Grok 4 Fast or Llama 3.1-405B better for coding?

They score almost the same on coding (32.5 vs 33.1); test both on your own repository before choosing.

### How many benchmarks do Grok 4 Fast and Llama 3.1-405B share?

23 benchmarks have published results for both models. Grok 4 Fast has 30 scored results on Noometry and Llama 3.1-405B has 42.