Model comparison
GPT-5.1-Codex vs Grok 4.1 Fast
Grok 4.1 Fast is the stronger model overall, scoring 41.4 to 38.6 on the Noometry Index.
Last verified . 3 shared benchmarks.
Summary
- They share 3 benchmarks with published results for both. GPT-5.1-Codex scores higher in 2 categories and Grok 4.1 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 34.1.
- The biggest single-benchmark swing is ProofBench: 9% for GPT-5.1-Codex and 4% for Grok 4.1 Fast.
- Grok 4.1 Fast is cheaper at $0.20 / $0.50 per million input/output tokens, against $1.25 / $10 for GPT-5.1-Codex.
- GPT-5.1-Codex accepts more context: 400K tokens versus 128K.
Side by side
| GPT-5.1-Codex | Grok 4.1 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 38.6 | 41.4 |
| Released | 2025-11-12 | 2025-06-27 |
| Weights | Proprietary | Proprietary |
| Context window | 400K | 128K |
| Max output | 128K | 30K |
| Input $ / M tokens | $1.25 | $0.20 |
| Output $ / M tokens | $10 | $0.50 |
| Results tracked | 6 | 32 |
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Category by category
Coding GPT-5.1-Codex leads
GPT-5.1-Codex: 41.9 (#116), Grok 4.1 Fast: 34.1 (#245)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena WebDev | 1337 | 1242 |
| ALE-Bench | 1,245 | 394.93 |
| SWE-bench Verified (bash only) | 66% | — |
| LMArena Coding | — | 1411 |
Agentic & Tool Use GPT-5.1-Codex leads
GPT-5.1-Codex: 38.0 (#33), Grok 4.1 Fast: 36.3 (#39)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| Terminal-Bench | 60.4% | — |
| Berkeley Function Calling Leaderboard | — | 69.6% |
| τ²-bench Banking | — | 13.1% |
| LMArena Search | — | 1171 |
| METR Time Horizons | 70.8% | — |
| Vending-Bench 2 | — | 1,107 |
Reasoning Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 43.4 (#49)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| SimpleBench | — | 56% |
| NYT Connections (extended) | — | 87.4% |
| LMArena Hard Prompts | — | 1407 |
| DTBench | — | 87.7% |
| ForecastBench | — | 61 |
Math Grok 4.1 Fast leads
GPT-5.1-Codex: 30.3 (#235), Grok 4.1 Fast: 31.9 (#221)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| ProofBench | 9% | 4% |
| MathArena Final-Answer Competitions | — | 60.9% |
| LMArena Math | — | 1408 |
Knowledge Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 33.1 (#207)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| Vectara Hallucination Rate | — | 17.8% |
| LMArena Expert | — | 1399 |
Multimodal Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 37.0 (#76)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Vision | — | 1201 |
Multilingual Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 51.0 (#114)
| Benchmark | GPT-5.1-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 Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 72.7 (#133)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Instruction Following | — | 1376 |
Long Context Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 42.4 (#126)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Longer Query | — | 1390 |
Writing & Preference Not comparable
GPT-5.1-Codex: —, Grok 4.1 Fast: 57.2 (#131)
| Benchmark | GPT-5.1-Codex | Grok 4.1 Fast |
|---|---|---|
| LMArena Text | — | 1408 |
| LMArena Creative Writing | — | 1394 |
| EQ-Bench Creative Writing | — | 1327 |
| LMArena Multi-Turn | — | 1389 |
Frequently asked questions
Is GPT-5.1-Codex better than Grok 4.1 Fast?
Grok 4.1 Fast is the stronger model overall, scoring 41.4 to 38.6 on the Noometry Index.
Which is cheaper, GPT-5.1-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-5.1-Codex lists at $1.25 and $10.
Is GPT-5.1-Codex or Grok 4.1 Fast better for coding?
GPT-5.1-Codex scores higher on coding benchmarks: 41.9 versus 34.1 in the Noometry coding category.
Which has the bigger context window?
GPT-5.1-Codex does, with 400K tokens against 128K.
How many benchmarks do GPT-5.1-Codex and Grok 4.1 Fast share?
3 benchmarks have published results for both models. GPT-5.1-Codex has 6 scored results on Noometry and Grok 4.1 Fast has 32.