# GPT-5.1-Codex vs Kimi K2 (Jul 2025)

> Kimi K2 (Jul 2025) is the stronger model overall, scoring 41.2 to 38.6 on the Noometry Index.

- Canonical page: https://noometry.com/compare/gpt-5-1-codex-vs-kimi-k2
- Last updated: 2026-10-11
- Shared benchmarks: 4

## Summary

- They share 4 benchmarks with published results for both. GPT-5.1-Codex scores higher in 1 category and Kimi K2 (Jul 2025) in 2 categories; 2 gaps are clear of the uncertainty.
- The widest gap is in math, where Kimi K2 (Jul 2025) leads 42.7 to 30.3.
- The biggest single-benchmark swing is Terminal-Bench: 60.4% for GPT-5.1-Codex and 35.7% for Kimi K2 (Jul 2025).
- Kimi K2 (Jul 2025) is cheaper at $0.57 / $2.30 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- GPT-5.1-Codex accepts more context: 400K tokens versus 262K.
- Kimi K2 (Jul 2025) has downloadable open weights; the other is API-only.

## Snapshot

| | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| Provider | OpenAI | Moonshot AI |
| Noometry Index | 38.6 | 41.2 |
| Rank | 186 | 140 |
| Context | 400K | 262K |
| Input $/M | $1.25 | $0.57 |
| Output $/M | $10 | $2.30 |
| Weights | Proprietary | Open |

## Coding

- GPT-5.1-Codex: 41.9 (#116)
- Kimi K2 (Jul 2025): 42.4 (#102)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | 63.4% |
| ALE-Bench | 1,245 | 597.5 |
| Aider Polyglot | — | 59.1% |
| LMArena WebDev | 1337 | — |
| GSO | — | 4.9% |
| WeirdML | — | 42.8% |
| LMArena Coding | — | 1399 |

## Agentic & Tool Use

- GPT-5.1-Codex: 38.0 (#33)
- Kimi K2 (Jul 2025): 32.4 (#64)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| Terminal-Bench | 60.4% | 35.7% |
| METR Time Horizons | 70.8% | 59.2% |
| Berkeley Function Calling Leaderboard | — | 59.1% |

## Reasoning

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 23.3 (#179)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| SimpleBench | — | 26.3% |
| Kagi LLM Benchmark | — | 64.4% |
| LMArena Hard Prompts | — | 1384 |
| Epoch Capabilities Index | — | 146.01 |
| ForecastBench | — | 60.2 |

## Math

- GPT-5.1-Codex: 30.3 (#235)
- Kimi K2 (Jul 2025): 42.7 (#83)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| ProofBench | 9% | — |
| Omni-MATH | — | 65.4% |
| LMArena Math | — | 1397 |
| FrontierMath (Feb 2025 set) | — | 21.4% |
| FrontierMath Tier 4 (v1) | — | 0% |

## Knowledge

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 37.3 (#157)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| MMLU-Pro | — | 81.9% |
| Confabulations | — | 20.4% |
| Vectara Hallucination Rate | — | 17.9% |
| GPQA (HELM) | — | 65.3% |
| LMArena Expert | — | 1365 |

## Multilingual

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 49.6 (#130)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Non-English | — | 1372 |
| LMArena Chinese | — | 1415 |
| LMArena French | — | 1379 |
| LMArena German | — | 1387 |
| LMArena Japanese | — | 1349 |
| LMArena Korean | — | 1325 |
| LMArena Russian | — | 1385 |
| LMArena Spanish | — | 1386 |

## Instruction Following

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 71.1 (#156)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| IFEval | — | 85% |
| LMArena Instruction Following | — | 1348 |

## Long Context

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 41.2 (#145)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| Fiction.LiveBench | — | 66.7% |
| CL-bench | — | 17.6% |
| LMArena Longer Query | — | 1353 |

## Writing & Preference

- GPT-5.1-Codex: —
- Kimi K2 (Jul 2025): 62.3 (#78)

| Benchmark | GPT-5.1-Codex | Kimi K2 (Jul 2025) |
|---|---|---|
| LMArena Text | — | 1380 |
| LMArena Creative Writing | — | 1350 |
| Short-Story Creative Writing | — | 85.6% |
| EQ-Bench Creative Writing | — | 1666 |
| WildBench | — | 86.2% |
| LMArena Multi-Turn | — | 1371 |

## FAQ

### Is GPT-5.1-Codex better than Kimi K2 (Jul 2025)?

Kimi K2 (Jul 2025) is the stronger model overall, scoring 41.2 to 38.6 on the Noometry Index.

### Which is cheaper, GPT-5.1-Codex or Kimi K2 (Jul 2025)?

Kimi K2 (Jul 2025) is cheaper. It lists at $0.57 per million input tokens and $2.30 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.

### Is GPT-5.1-Codex or Kimi K2 (Jul 2025) better for coding?

They score almost the same on coding (41.9 vs 42.4); test both on your own repository before choosing.

### Which has the bigger context window?

GPT-5.1-Codex does, with 400K tokens against 262K.

### How many benchmarks do GPT-5.1-Codex and Kimi K2 (Jul 2025) share?

4 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Kimi K2 (Jul 2025) has 42.