# GPT-5.3 Codex vs Llama 3.1-405B

> GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 30.4 on the Noometry Index.

- Canonical page: https://noometry.com/compare/gpt-5-3-codex-vs-llama-3-1-405b
- Last updated: 2026-10-10
- Shared benchmarks: 2

## Summary

- They share 2 benchmarks with published results for both. GPT-5.3 Codex scores higher in 2 categories and Llama 3.1-405B in 0 categories; 2 gaps are clear of the uncertainty.
- The widest gap is in agentic & tool use, where GPT-5.3 Codex leads 47.8 to 20.9.
- The biggest single-benchmark swing is WeirdML: 79.3% for GPT-5.3 Codex and 21.4% for Llama 3.1-405B.
- Llama 3.1-405B has downloadable open weights; the other is API-only.

## Snapshot

| | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| Provider | OpenAI | Meta |
| Noometry Index | 45.5 | 30.4 |
| Rank | 61 | 279 |
| Context | 400K | — |
| Input $/M | $1.75 | — |
| Output $/M | $14 | — |
| Weights | Proprietary | Open |

## Coding

- GPT-5.3 Codex: 48.5 (#51)
- Llama 3.1-405B: 32.7 (#257)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| WeirdML | 79.3% | 21.4% |
| SWE-bench Verified | 74.8% | — |
| LMArena WebDev | 1408 | — |
| LMArena Coding | — | 1291 |
| ALE-Bench | 1,655 | — |

## Agentic & Tool Use

- GPT-5.3 Codex: 47.8 (#9)
- Llama 3.1-405B: 20.9 (#131)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| Terminal-Bench | 78.4% | — |
| TheAgentCompany | — | 7.4% |
| Cybench | — | 7.5% |
| METR Time Horizons | 74.5% | — |
| Vending-Bench 2 | 5,940 | — |

## Reasoning

- GPT-5.3 Codex: —
- Llama 3.1-405B: 16.4 (#293)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| Epoch Capabilities Index | 156.84 | 128.76 |
| SimpleBench | — | 23% |
| Kagi LLM Benchmark | — | 45% |
| LMArena Hard Prompts | — | 1270 |
| DTBench | — | 61.4% |
| BIG-Bench Hard | — | 82.9% |
| ForecastBench | — | 59.9 |
| HellaSwag | — | 89.2% |
| PIQA | — | 85.9% |
| WinoGrande | — | 89.2% |

## Math

- GPT-5.3 Codex: —
- Llama 3.1-405B: 17.3 (#283)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| OTIS Mock AIME 2024-2025 | — | 9.7% |
| Omni-MATH | — | 24.9% |
| LMArena Math | — | 1281 |
| MATH Level 5 | — | 49.8% |

## Knowledge

- GPT-5.3 Codex: —
- Llama 3.1-405B: 30.4 (#221)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| GPQA Diamond | — | 50.9% |
| MMLU-Pro | — | 72.3% |
| Confabulations | — | 17.6% |
| GPQA (HELM) | — | 52.2% |
| LMArena Expert | — | 1243 |
| ARC (AI2) Challenge | — | 95.3% |
| MMLU | — | 84.5% |
| TriviaQA | — | 82.7% |

## Multilingual

- GPT-5.3 Codex: —
- Llama 3.1-405B: 40.9 (#209)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| LMArena Non-English | — | 1248 |
| LMArena Chinese | — | 1242 |
| LMArena French | — | 1278 |
| LMArena German | — | 1252 |
| LMArena Japanese | — | 1208 |
| LMArena Korean | — | 1184 |
| LMArena Russian | — | 1265 |
| LMArena Spanish | — | 1259 |

## Instruction Following

- GPT-5.3 Codex: —
- Llama 3.1-405B: 66.1 (#209)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| IFEval | — | 81.1% |
| LMArena Instruction Following | — | 1259 |

## Long Context

- GPT-5.3 Codex: —
- Llama 3.1-405B: 38.4 (#192)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| LMArena Longer Query | — | 1266 |

## Writing & Preference

- GPT-5.3 Codex: —
- Llama 3.1-405B: 39.1 (#246)

| Benchmark | GPT-5.3 Codex | Llama 3.1-405B |
|---|---|---|
| LMArena Text | — | 1284 |
| LMArena Creative Writing | — | 1262 |
| EQ-Bench Creative Writing | — | 870 |
| WildBench | — | 78.3% |
| LMArena Multi-Turn | — | 1297 |

## FAQ

### Is GPT-5.3 Codex better than Llama 3.1-405B?

GPT-5.3 Codex is the stronger model overall, scoring 45.5 to 30.4 on the Noometry Index.

### Is GPT-5.3 Codex or Llama 3.1-405B better for coding?

GPT-5.3 Codex scores higher on coding benchmarks: 48.5 versus 32.7 in the Noometry coding category.

### How many benchmarks do GPT-5.3 Codex and Llama 3.1-405B share?

2 benchmarks have published results for both models. GPT-5.3 Codex has 8 scored results on Noometry and Llama 3.1-405B has 42.