# GPT-5-Codex vs Grok 4.1 Fast

> Grok 4.1 Fast is the stronger model overall, scoring 41.4 to 37.9 on the Noometry Index.

- Canonical page: https://noometry.com/compare/gpt-5-codex-vs-grok-4-1-fast
- Last updated: 2026-10-11
- Shared benchmarks: 0

## Summary

- The widest gap is in reasoning, where Grok 4.1 Fast leads 43.4 to 30.9.
- Grok 4.1 Fast is cheaper at $0.20 / $0.50 per million input/output tokens, against $1.25 / $10 for GPT-5-Codex.
- GPT-5-Codex accepts more context: 400K tokens versus 128K.

## Snapshot

| | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 37.9 | 41.4 |
| Rank | 192 | 136 |
| Context | 400K | 128K |
| Input $/M | $1.25 | $0.20 |
| Output $/M | $10 | $0.50 |
| Weights | Proprietary | Proprietary |

## Coding

- GPT-5-Codex: 42.4 (#103)
- Grok 4.1 Fast: 34.1 (#245)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena WebDev | — | 1242 |
| WeirdML | 54.5% | — |
| LMArena Coding | — | 1411 |
| ALE-Bench | — | 394.93 |

## Agentic & Tool Use

- GPT-5-Codex: 31.0 (#72)
- Grok 4.1 Fast: 36.3 (#39)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| Terminal-Bench | 44.3% | — |
| Berkeley Function Calling Leaderboard | — | 69.6% |
| τ²-bench Banking | — | 13.1% |
| LMArena Search | — | 1171 |
| Vending-Bench 2 | — | 1,107 |

## Reasoning

- GPT-5-Codex: 30.9 (#83)
- Grok 4.1 Fast: 43.4 (#49)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| SimpleBench | — | 56% |
| Kagi LLM Benchmark | 70.3% | — |
| NYT Connections (extended) | — | 87.4% |
| LMArena Hard Prompts | — | 1407 |
| DTBench | — | 87.7% |
| ForecastBench | — | 61 |

## Math

- GPT-5-Codex: —
- Grok 4.1 Fast: 31.9 (#221)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| MathArena Final-Answer Competitions | — | 60.9% |
| ProofBench | — | 4% |
| LMArena Math | — | 1408 |

## Knowledge

- GPT-5-Codex: —
- Grok 4.1 Fast: 33.1 (#207)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| Vectara Hallucination Rate | — | 17.8% |
| LMArena Expert | — | 1399 |

## Multimodal

- GPT-5-Codex: —
- Grok 4.1 Fast: 37.0 (#76)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Vision | — | 1201 |

## Multilingual

- GPT-5-Codex: —
- Grok 4.1 Fast: 51.0 (#114)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Non-English | — | 1391 |
| LMArena Chinese | — | 1441 |
| LMArena French | — | 1415 |
| LMArena German | — | 1404 |
| LMArena Japanese | — | 1349 |
| LMArena Korean | — | 1361 |
| LMArena Russian | — | 1387 |
| LMArena Spanish | — | 1413 |

## Instruction Following

- GPT-5-Codex: —
- Grok 4.1 Fast: 72.7 (#133)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Instruction Following | — | 1376 |

## Long Context

- GPT-5-Codex: —
- Grok 4.1 Fast: 42.4 (#126)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Longer Query | — | 1390 |

## Writing & Preference

- GPT-5-Codex: —
- Grok 4.1 Fast: 57.2 (#131)

| Benchmark | GPT-5-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Text | — | 1408 |
| LMArena Creative Writing | — | 1394 |
| EQ-Bench Creative Writing | — | 1327 |
| LMArena Multi-Turn | — | 1389 |

## FAQ

### Is GPT-5-Codex better than Grok 4.1 Fast?

Grok 4.1 Fast is the stronger model overall, scoring 41.4 to 37.9 on the Noometry Index.

### Which is cheaper, GPT-5-Codex or Grok 4.1 Fast?

Grok 4.1 Fast is cheaper. It lists at $0.20 per million input tokens and $0.50 per million output tokens; GPT-5-Codex lists at $1.25 and $10.

### Is GPT-5-Codex or Grok 4.1 Fast better for coding?

GPT-5-Codex scores higher on coding benchmarks: 42.4 versus 34.1 in the Noometry coding category.

### Which has the bigger context window?

GPT-5-Codex does, with 400K tokens against 128K.

### How many benchmarks do GPT-5-Codex and Grok 4.1 Fast share?

0 benchmarks have published results for both models. GPT-5-Codex has 3 scored results on Noometry and Grok 4.1 Fast has 32.