Model comparison
GPT-5.6 Luna vs Grok 4.1 Fast
GPT-5.6 Luna is the stronger model overall, scoring 54.6 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 1.6× less per token, which makes it the better buy when GPT-5.6 Luna's lead doesn't matter for your workload.
Last verified . 26 shared benchmarks.
Summary
- They share 26 benchmarks with published results for both. GPT-5.6 Luna scores higher in 9 categories and Grok 4.1 Fast in 1 category; 10 gaps are clear of the uncertainty.
- The widest gap is in math, where GPT-5.6 Luna leads 77.7 to 31.9.
- The biggest single-benchmark swing is ProofBench: 60% for GPT-5.6 Luna and 4% for Grok 4.1 Fast.
- Grok 4.1 Fast is cheaper at $0.20 / $0.50 per million input/output tokens, against $0.20 / $1.20 for GPT-5.6 Luna.
- GPT-5.6 Luna accepts more context: 1.05M tokens versus 128K.
Side by side
| GPT-5.6 Luna | Grok 4.1 Fast | |
|---|---|---|
| Provider | OpenAI | xAI |
| Noometry Index | 54.6 | 41.4 |
| Released | 2026-07-09 | 2025-06-27 |
| Weights | Proprietary | Proprietary |
| Context window | 1.05M | 128K |
| Max output | 128K | 30K |
| Input $ / M tokens | $0.20 | $0.20 |
| Output $ / M tokens | $1.20 | $0.50 |
| Results tracked | 52 | 32 |
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Category by category
Coding GPT-5.6 Luna leads
GPT-5.6 Luna: 54.5 (#28), Grok 4.1 Fast: 34.1 (#245)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena WebDev | 1519 | 1242 |
| LMArena Coding | 1466 | 1411 |
| ALE-Bench | 1,667 | 394.93 |
| DeepSWE | 67.2% | — |
| FrontierCode | 39.8% | — |
| CursorBench | 35.9% | — |
| SciCode | 53.6% | — |
| WeirdML | 60.9% | — |
Agentic & Tool Use Grok 4.1 Fast leads
GPT-5.6 Luna: 34.4 (#45), Grok 4.1 Fast: 36.3 (#39)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| Vending-Bench 2 | 4,095 | 1,107 |
| APEX-Agents | 43% | — |
| Berkeley Function Calling Leaderboard | — | 69.6% |
| τ²-bench Banking | — | 13.1% |
| BALROG | 45.6% | — |
| GDP.pdf | 22.7% | — |
| LMArena Search | — | 1171 |
Reasoning GPT-5.6 Luna leads
GPT-5.6 Luna: 47.6 (#43), Grok 4.1 Fast: 43.4 (#49)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| SimpleBench | 46.8% | 56% |
| NYT Connections (extended) | 69.4% | 87.4% |
| LMArena Hard Prompts | 1451 | 1407 |
| DTBench | 89.1% | 87.7% |
| ARC-AGI-2 | 59.5% | — |
| Kagi LLM Benchmark | 49.1% | — |
| ARC-AGI-1 | 88% | — |
| CritPt | 20.6% | — |
| Chess Puzzles | 40% | — |
| Mystery Game Puzzles | 21% | — |
| LMCA | 48.5% | — |
| Surface Evolver Bench | 61.9% | — |
| Epoch Capabilities Index | 156.39 | — |
| ForecastBench | — | 61 |
Math GPT-5.6 Luna leads
GPT-5.6 Luna: 77.7 (#14), Grok 4.1 Fast: 31.9 (#221)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| ProofBench | 60% | 4% |
| LMArena Math | 1458 | 1408 |
| FrontierMath (Tiers 1-3) | 82.1% | — |
| FrontierMath Tier 4 | 61% | — |
| MathArena Final-Answer Competitions | — | 60.9% |
| OTIS Mock AIME 2024-2025 | 98.3% | — |
Knowledge GPT-5.6 Luna leads
GPT-5.6 Luna: 58.5 (#34), Grok 4.1 Fast: 33.1 (#207)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Expert | 1478 | 1399 |
| GPQA Diamond | 91.6% | — |
| SimpleQA Verified | 41% | — |
| Vectara Hallucination Rate | — | 17.8% |
Multimodal GPT-5.6 Luna leads
GPT-5.6 Luna: 42.7 (#28), Grok 4.1 Fast: 37.0 (#76)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Vision | 1258 | 1201 |
| Blueprint-Bench 2 | 22.6% | — |
| Furniture Assembly | 42.5% | — |
| LMArena Document | 1457 | — |
Multilingual GPT-5.6 Luna leads
GPT-5.6 Luna: 52.8 (#78), Grok 4.1 Fast: 51.0 (#114)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Non-English | 1417 | 1391 |
| LMArena Chinese | 1470 | 1441 |
| LMArena French | 1456 | 1415 |
| LMArena German | 1454 | 1404 |
| LMArena Japanese | 1411 | 1349 |
| LMArena Korean | 1415 | 1361 |
| LMArena Russian | 1428 | 1387 |
| LMArena Spanish | 1448 | 1413 |
Instruction Following GPT-5.6 Luna leads
GPT-5.6 Luna: 75.6 (#57), Grok 4.1 Fast: 72.7 (#133)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Instruction Following | 1437 | 1376 |
Long Context GPT-5.6 Luna leads
GPT-5.6 Luna: 43.9 (#82), Grok 4.1 Fast: 42.4 (#126)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Longer Query | 1436 | 1390 |
Writing & Preference GPT-5.6 Luna leads
GPT-5.6 Luna: 68.0 (#29), Grok 4.1 Fast: 57.2 (#131)
| Benchmark | GPT-5.6 Luna | Grok 4.1 Fast |
|---|---|---|
| LMArena Text | 1431 | 1408 |
| LMArena Creative Writing | 1396 | 1394 |
| EQ-Bench Creative Writing | 1829 | 1327 |
| LMArena Multi-Turn | 1434 | 1389 |
| EQ-Bench 4 | 1156 | — |
Frequently asked questions
Is GPT-5.6 Luna better than Grok 4.1 Fast?
GPT-5.6 Luna is the stronger model overall, scoring 54.6 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 1.6× less per token, which makes it the better buy when GPT-5.6 Luna's lead doesn't matter for your workload.
Which is cheaper, GPT-5.6 Luna 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-5.6 Luna lists at $0.20 and $1.20.
Is GPT-5.6 Luna or Grok 4.1 Fast better for coding?
GPT-5.6 Luna scores higher on coding benchmarks: 54.5 versus 34.1 in the Noometry coding category.
Which has the bigger context window?
GPT-5.6 Luna does, with 1.05M tokens against 128K.
How many benchmarks do GPT-5.6 Luna and Grok 4.1 Fast share?
26 benchmarks have published results for both models. GPT-5.6 Luna has 52 scored results on Noometry and Grok 4.1 Fast has 32.