Model comparison
GPT-5.1-Codex vs Grok 4 Fast
GPT-5.1-Codex and Grok 4 Fast score almost the same on the Noometry Index (38.6 vs 39.4), so choose on price, context window or the category you care about most.
Last verified . 1 shared benchmarks.
Summary
- They share 1 benchmark with published results for both. GPT-5.1-Codex scores higher in 2 categories and Grok 4 Fast in 1 category; 3 gaps are clear of the uncertainty.
- The widest gap is in coding, where GPT-5.1-Codex leads 41.9 to 32.5.
Side by side
| GPT-5.1-Codex | Grok 4 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 38.6 | 39.4 |
| Released | 2025-11-12 | 2025-09-19 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | — |
| Max output | 128K | — |
| Input $ / M tokens | $1.25 | — |
| Output $ / M tokens | $10 | — |
| Results tracked | 6 | 30 |
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Category by category
Coding GPT-5.1-Codex leads
GPT-5.1-Codex: 41.9 (#116), Grok 4 Fast: 32.5 (#271)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| LMArena WebDev | 1337 | 1159 |
| SWE-bench Verified (bash only) | 66% | — |
| WeirdML | — | 42.9% |
| LMArena Coding | — | 1429 |
| ALE-Bench | 1,245 | — |
Agentic & Tool Use GPT-5.1-Codex leads
GPT-5.1-Codex: 38.0 (#33), Grok 4 Fast: 29.5 (#86)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| τ²-bench Banking | — | 15.7% |
| Cybench | — | 30% |
| LMArena Search | — | 1171 |
| METR Time Horizons | 70.8% | — |
Reasoning Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 22.2 (#201)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| ARC-AGI-2 | — | 5.3% |
| Kagi LLM Benchmark | — | 66.1% |
| ARC-AGI-1 | — | 48.5% |
| LMArena Hard Prompts | — | 1412 |
| DTBench | — | 82.7% |
| Epoch Capabilities Index | — | 144.2 |
| ForecastBench | — | 60.5 |
Math Grok 4 Fast leads
GPT-5.1-Codex: 30.3 (#235), Grok 4 Fast: 38.9 (#123)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| ProofBench | 9% | — |
| LMArena Math | — | 1419 |
Knowledge Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 32.0 (#214)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| Vectara Hallucination Rate | — | 19.7% |
| LMArena Expert | — | 1411 |
Multilingual Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 51.3 (#111)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| LMArena Non-English | — | 1396 |
| LMArena Chinese | — | 1457 |
| LMArena French | — | 1431 |
| LMArena German | — | 1383 |
| LMArena Japanese | — | 1352 |
| LMArena Korean | — | 1357 |
| LMArena Russian | — | 1389 |
| LMArena Spanish | — | 1415 |
Instruction Following Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 73.2 (#121)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| LMArena Instruction Following | — | 1387 |
Long Context Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 63.2 (#3)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| Fiction.LiveBench | — | 94.4% |
| LMArena Longer Query | — | 1415 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, Grok 4 Fast: 60.0 (#102)
| Benchmark | GPT-5.1-Codex | Grok 4 Fast |
|---|---|---|
| LMArena Text | — | 1407 |
| LMArena Creative Writing | — | 1387 |
| LMArena Multi-Turn | — | 1414 |
Frequently asked questions
Is GPT-5.1-Codex better than Grok 4 Fast?
GPT-5.1-Codex and Grok 4 Fast score almost the same on the Noometry Index (38.6 vs 39.4), so choose on price, context window or the category you care about most.
Is GPT-5.1-Codex or Grok 4 Fast better for coding?
GPT-5.1-Codex scores higher on coding benchmarks: 41.9 versus 32.5 in the Noometry coding category.
How many benchmarks do GPT-5.1-Codex and Grok 4 Fast share?
1 benchmark has published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Grok 4 Fast has 30.