# GPT-5.1-Codex vs Kimi K2.5

> Kimi K2.5 is the stronger model overall, scoring 47.8 to 38.2 on the Noometry Index.

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

## Summary

- They share 4 benchmarks with published results for both. GPT-5.1-Codex scores higher in 1 category and Kimi K2.5 in 2 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in math, where Kimi K2.5 leads 50.3 to 29.3.
- The biggest single-benchmark swing is Terminal-Bench: 60.4% for GPT-5.1-Codex and 43.2% for Kimi K2.5.
- Kimi K2.5 is cheaper at $0.45 / $2.25 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 K2.5 has downloadable open weights; the other is API-only.

## Snapshot

| | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| Provider | OpenAI | Moonshot AI |
| Noometry Index | 38.2 | 47.8 |
| Rank | 178 | 50 |
| Context | 400K | 262K |
| Input $/M | $1.25 | $0.45 |
| Output $/M | $10 | $2.25 |
| Weights | Proprietary | Open |

## Coding

- GPT-5.1-Codex: 41.7 (#107)
- Kimi K2.5: 48.7 (#48)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| SWE-bench Verified (bash only) | 66% | 70.8% |
| LMArena WebDev | 1337 | 1436 |
| ALE-Bench | 1,245 | 821.65 |
| SWE-bench Verified | — | 73.8% |
| SWE-bench Multilingual | — | 67.3% |
| SciCode | — | 49% |
| WeirdML | — | 45.6% |
| LMArena Coding | — | 1474 |

## Agentic & Tool Use

- GPT-5.1-Codex: 37.8 (#32)
- Kimi K2.5: 34.0 (#44)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| Terminal-Bench | 60.4% | 43.2% |
| OSWorld | — | 63.3% |
| METR Time Horizons | 70.8% | — |
| Vending-Bench 2 | — | 1,198 |

## Reasoning

- GPT-5.1-Codex: —
- Kimi K2.5: 31.2 (#74)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| ARC-AGI-2 | — | 11.8% |
| SimpleBench | — | 46.8% |
| Kagi LLM Benchmark | — | 78.5% |
| NYT Connections (extended) | — | 69.9% |
| ARC-AGI-1 | — | 65.3% |
| CritPt | — | 3.1% |
| Chess Puzzles | — | 12% |
| EnigmaEval | — | 3.4% |
| Thematic Generalization | — | 69.4% |
| LMArena Hard Prompts | — | 1454 |
| Epoch Capabilities Index | — | 148.05 |

## Math

- GPT-5.1-Codex: 29.3 (#218)
- Kimi K2.5: 50.3 (#46)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| MathArena Final-Answer Competitions | — | 62.3% |
| OTIS Mock AIME 2024-2025 | — | 92.2% |
| ProofBench | 9% | — |
| LMArena Math | — | 1470 |
| FrontierMath (Feb 2025 set) | — | 27.9% |
| FrontierMath Tier 4 (v1) | — | 4.2% |

## Knowledge

- GPT-5.1-Codex: —
- Kimi K2.5: 53.6 (#52)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| GPQA Diamond | — | 87.6% |
| Humanity's Last Exam | — | 24.4% |
| SimpleQA Verified | — | 34.3% |
| Vectara Hallucination Rate | — | 14.2% |
| LMArena Expert | — | 1466 |

## Multimodal

- GPT-5.1-Codex: —
- Kimi K2.5: 40.4 (#37)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| LMArena Vision | — | 1269 |
| LMArena Document | — | 1430 |

## Multilingual

- GPT-5.1-Codex: —
- Kimi K2.5: 54.1 (#50)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| LMArena Non-English | — | 1433 |
| LMArena Chinese | — | 1495 |
| LMArena French | — | 1454 |
| LMArena German | — | 1441 |
| LMArena Japanese | — | 1422 |
| LMArena Korean | — | 1412 |
| LMArena Russian | — | 1436 |
| LMArena Spanish | — | 1450 |

## Instruction Following

- GPT-5.1-Codex: —
- Kimi K2.5: 75.5 (#60)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| LMArena Instruction Following | — | 1431 |

## Long Context

- GPT-5.1-Codex: —
- Kimi K2.5: 52.1 (#7)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| Fiction.LiveBench | — | 86.1% |
| CL-bench | — | 19.3% |
| CL-bench Life | — | 13.2% |
| LMArena Longer Query | — | 1445 |

## Writing & Preference

- GPT-5.1-Codex: —
- Kimi K2.5: 65.3 (#51)

| Benchmark | GPT-5.1-Codex | Kimi K2.5 |
|---|---|---|
| LMArena Text | — | 1445 |
| LMArena Creative Writing | — | 1423 |
| EQ-Bench Creative Writing | — | 1579 |
| LMArena Multi-Turn | — | 1444 |

## FAQ

### Is GPT-5.1-Codex better than Kimi K2.5?

Kimi K2.5 is the stronger model overall, scoring 47.8 to 38.2 on the Noometry Index.

### Which is cheaper, GPT-5.1-Codex or Kimi K2.5?

Kimi K2.5 is cheaper. It lists at $0.45 per million input tokens and $2.25 per million output tokens; GPT-5.1-Codex lists at $1.25 and $10.

### Is GPT-5.1-Codex or Kimi K2.5 better for coding?

Kimi K2.5 scores higher on coding benchmarks: 48.7 versus 41.7 in the Noometry coding category.

### 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 K2.5 share?

4 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Kimi K2.5 has 51.