Model comparison
Grok 4 Fast vs Kimi K2.5 Instant
Kimi K2.5 Instant is the stronger model overall, scoring 43.6 to 39.4 on the Noometry Index.
Last verified . 17 shared benchmarks.
Summary
- They share 17 benchmarks with published results for both. Grok 4 Fast scores higher in 1 category and Kimi K2.5 Instant in 7 categories; 5 gaps are clear of the uncertainty.
- The widest gap is in long context, where Grok 4 Fast leads 63.2 to 43.9.
- Kimi K2.5 Instant has downloadable open weights; the other is API-only.
Side by side
| Grok 4 Fast | Kimi K2.5 Instant | |
|---|---|---|
| Provider | xAI | Moonshot AI |
| Noometry Index | 39.4 | 43.6 |
| Released | 2025-09-19 | — |
| Weights | Proprietary | Open |
| Context window | — | — |
| Max output | — | — |
| Input $ / M tokens | — | — |
| Output $ / M tokens | — | — |
| Results tracked | 30 | 18 |
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Category by category
Coding Kimi K2.5 Instant leads
Grok 4 Fast: 32.5 (#271), Kimi K2.5 Instant: 42.6 (#97)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena WebDev | 1159 | 1404 |
| LMArena Coding | 1429 | 1484 |
| WeirdML | 42.9% | — |
Agentic & Tool Use Not comparable
Grok 4 Fast: 29.5 (#86), Kimi K2.5 Instant: —
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| τ²-bench Banking | 15.7% | — |
| Cybench | 30% | — |
| LMArena Search | 1171 | — |
Reasoning Kimi K2.5 Instant leads
Grok 4 Fast: 22.2 (#201), Kimi K2.5 Instant: 29.7 (#90)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Hard Prompts | 1412 | 1443 |
| ARC-AGI-2 | 5.3% | — |
| Kagi LLM Benchmark | 66.1% | — |
| ARC-AGI-1 | 48.5% | — |
| DTBench | 82.7% | — |
| Epoch Capabilities Index | 144.2 | — |
| ForecastBench | 60.5 | — |
Math Too close to call
Grok 4 Fast: 38.9 (#123), Kimi K2.5 Instant: 39.4 (#105)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Math | 1419 | 1442 |
Knowledge Kimi K2.5 Instant leads
Grok 4 Fast: 32.0 (#214), Kimi K2.5 Instant: 40.2 (#123)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Expert | 1411 | 1440 |
| Vectara Hallucination Rate | 19.7% | — |
Multimodal Not comparable
Grok 4 Fast: —, Kimi K2.5 Instant: 40.2 (#50)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Vision | — | 1254 |
Multilingual Too close to call
Grok 4 Fast: 51.3 (#111), Kimi K2.5 Instant: 52.0 (#94)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Non-English | 1396 | 1406 |
| LMArena Chinese | 1457 | 1449 |
| LMArena French | 1431 | 1403 |
| LMArena German | 1383 | 1413 |
| LMArena Korean | 1357 | 1378 |
| LMArena Russian | 1389 | 1404 |
| LMArena Spanish | 1415 | 1447 |
| LMArena Japanese | 1352 | — |
Instruction Following Kimi K2.5 Instant leads
Grok 4 Fast: 73.2 (#121), Kimi K2.5 Instant: 75.3 (#65)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Instruction Following | 1387 | 1430 |
Long Context Grok 4 Fast leads
Grok 4 Fast: 63.2 (#3), Kimi K2.5 Instant: 43.9 (#83)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Longer Query | 1415 | 1435 |
| Fiction.LiveBench | 94.4% | — |
Writing & Preference Too close to call
Grok 4 Fast: 60.0 (#102), Kimi K2.5 Instant: 60.6 (#95)
| Benchmark | Grok 4 Fast | Kimi K2.5 Instant |
|---|---|---|
| LMArena Text | 1407 | 1420 |
| LMArena Creative Writing | 1387 | 1381 |
| LMArena Multi-Turn | 1414 | 1427 |
Frequently asked questions
Is Grok 4 Fast better than Kimi K2.5 Instant?
Kimi K2.5 Instant is the stronger model overall, scoring 43.6 to 39.4 on the Noometry Index.
Is Grok 4 Fast or Kimi K2.5 Instant better for coding?
Kimi K2.5 Instant scores higher on coding benchmarks: 42.6 versus 32.5 in the Noometry coding category.
How many benchmarks do Grok 4 Fast and Kimi K2.5 Instant share?
17 benchmarks have published results for both models. Grok 4 Fast has 30 scored results on Noometry and Kimi K2.5 Instant has 18.