Model comparison
Claude Fable 5.1 vs Grok 4.1 Fast
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 73× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.
Last verified . 25 shared benchmarks.
Summary
- They share 25 benchmarks with published results for both. Claude Fable 5.1 scores higher in 10 categories and Grok 4.1 Fast in 0 categories; 10 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Fable 5.1 leads 89.6 to 31.9.
- The biggest single-benchmark swing is ProofBench: 100% for Claude Fable 5.1 and 4% for Grok 4.1 Fast.
- Grok 4.1 Fast is cheaper at $0.20 / $0.50 per million input/output tokens, against $10 / $50 for Claude Fable 5.1.
- Claude Fable 5.1 accepts more context: 1M tokens versus 128K.
Side by side
| Claude Fable 5.1 | Grok 4.1 Fast | |
|---|---|---|
| Provider | Anthropic | xAI |
| Noometry Index | 69.0 | 41.4 |
| Released | 2026-09-01 | 2025-06-27 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 128K |
| Max output | 128K | 30K |
| Input $ / M tokens | $10 | $0.20 |
| Output $ / M tokens | $50 | $0.50 |
| Results tracked | 52 | 32 |
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Category by category
Coding Claude Fable 5.1 leads
Claude Fable 5.1: 74.7 (#1), Grok 4.1 Fast: 34.1 (#245)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena WebDev | 1744 | 1242 |
| LMArena Coding | 1528 | 1411 |
| ALE-Bench | 2,143 | 394.93 |
| FrontierCode | 50.9% | — |
| CursorBench | 51.8% | — |
| FrontierSWE | 56.3% | — |
| SciCode | 63.1% | — |
| GSO | 88.2% | — |
| WeirdML | 92.9% | — |
| MirrorCode | 73.3% | — |
Agentic & Tool Use Claude Fable 5.1 leads
Claude Fable 5.1: 50.7 (#5), Grok 4.1 Fast: 36.3 (#39)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| Vending-Bench 2 | 5,422 | 1,107 |
| APEX-Agents | 68.6% | — |
| Berkeley Function Calling Leaderboard | — | 69.6% |
| Remote Labor Index | 17.9% | — |
| τ²-bench Banking | — | 13.1% |
| GDP.pdf | 29.6% | — |
| LMArena Search | — | 1171 |
Reasoning Claude Fable 5.1 leads
Claude Fable 5.1: 76.7 (#7), Grok 4.1 Fast: 43.4 (#49)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| NYT Connections (extended) | 90% | 87.4% |
| LMArena Hard Prompts | 1526 | 1407 |
| DTBench | 97.6% | 87.7% |
| ARC-AGI-2 | 90% | — |
| SimpleBench | — | 56% |
| ARC-AGI-1 | 97.5% | — |
| CritPt | 31.1% | — |
| Chess Puzzles | 47% | — |
| EBR-Bench | 57.1% | — |
| Mystery Game Puzzles | 58% | — |
| LMCA | 65.5% | — |
| Epoch Capabilities Index | 164.7 | — |
| ForecastBench | — | 61 |
Math Claude Fable 5.1 leads
Claude Fable 5.1: 89.6 (#4), Grok 4.1 Fast: 31.9 (#221)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| ProofBench | 100% | 4% |
| LMArena Math | 1525 | 1408 |
| FrontierMath (Tiers 1-3) | 90.2% | — |
| FrontierMath Tier 4 | 87.8% | — |
| MathArena Final-Answer Competitions | — | 60.9% |
| OTIS Mock AIME 2024-2025 | 100% | — |
| FrontierMath Erdős | 0% | — |
Knowledge Claude Fable 5.1 leads
Claude Fable 5.1: 69.6 (#6), Grok 4.1 Fast: 33.1 (#207)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Expert | 1535 | 1399 |
| Humanity's Last Exam | 46.5% | — |
| SimpleQA Verified | 70.8% | — |
| Vectara Hallucination Rate | — | 17.8% |
Multimodal Claude Fable 5.1 leads
Claude Fable 5.1: 53.9 (#4), Grok 4.1 Fast: 37.0 (#76)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Vision | 1318 | 1201 |
| Blueprint-Bench 2 | 41.9% | — |
| Furniture Assembly | 70% | — |
| LMArena Document | 1513 | — |
Multilingual Claude Fable 5.1 leads
Claude Fable 5.1: 59.1 (#3), Grok 4.1 Fast: 51.0 (#114)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Non-English | 1507 | 1391 |
| LMArena Chinese | 1586 | 1441 |
| LMArena French | 1525 | 1415 |
| LMArena German | 1500 | 1404 |
| LMArena Japanese | 1543 | 1349 |
| LMArena Korean | 1534 | 1361 |
| LMArena Russian | 1521 | 1387 |
| LMArena Spanish | 1516 | 1413 |
Instruction Following Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#6), Grok 4.1 Fast: 72.7 (#133)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Instruction Following | 1517 | 1376 |
Long Context Claude Fable 5.1 leads
Claude Fable 5.1: 46.7 (#20), Grok 4.1 Fast: 42.4 (#126)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Longer Query | 1522 | 1390 |
Writing & Preference Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#2), Grok 4.1 Fast: 57.2 (#131)
| Benchmark | Claude Fable 5.1 | Grok 4.1 Fast |
|---|---|---|
| LMArena Text | 1510 | 1408 |
| LMArena Creative Writing | 1507 | 1394 |
| EQ-Bench Creative Writing | 2162 | 1327 |
| LMArena Multi-Turn | 1492 | 1389 |
Frequently asked questions
Is Claude Fable 5.1 better than Grok 4.1 Fast?
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 41.4 on the Noometry Index. Grok 4.1 Fast costs 73× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.
Which is cheaper, Claude Fable 5.1 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; Claude Fable 5.1 lists at $10 and $50.
Is Claude Fable 5.1 or Grok 4.1 Fast better for coding?
Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 34.1 in the Noometry coding category.
Which has the bigger context window?
Claude Fable 5.1 does, with 1M tokens against 128K.
How many benchmarks do Claude Fable 5.1 and Grok 4.1 Fast share?
25 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and Grok 4.1 Fast has 32.