Model comparison
Claude Fable 5.1 vs Step 5 Preview
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 47.9 on the Noometry Index. Step 5 Preview costs 14× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.
Last verified . 18 shared benchmarks.
StepFunSummary
- They share 18 benchmarks with published results for both. Claude Fable 5.1 scores higher in 9 categories and Step 5 Preview in 0 categories; 9 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Fable 5.1 leads 89.6 to 46.1.
- The biggest single-benchmark swing is ProofBench: 100% for Claude Fable 5.1 and 42% for Step 5 Preview.
- Step 5 Preview is cheaper at $1 / $2.70 per million input/output tokens, against $10 / $50 for Claude Fable 5.1.
- Step 5 Preview accepts more context: 1.02M tokens versus 1M.
Side by side
| Claude Fable 5.1 | Step 5 Preview | |
|---|---|---|
| Provider | Anthropic | StepFun |
| Noometry Index | 69.0 | 47.9 |
| Released | 2026-09-01 | 2026-09-16 |
| Weights | Proprietary | Proprietary |
| Context window | 1M | 1.02M |
| Max output | 128K | 66K |
| Input $ / M tokens | $10 | $1 |
| Output $ / M tokens | $50 | $2.70 |
| Results tracked | 52 | 18 |
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Category by category
Coding Claude Fable 5.1 leads
Claude Fable 5.1: 74.7 (#1), Step 5 Preview: 51.8 (#36)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena WebDev | 1744 | 1564 |
| SciCode | 63.1% | 58.9% |
| LMArena Coding | 1528 | 1480 |
| FrontierCode | 50.9% | — |
| CursorBench | 51.8% | — |
| FrontierSWE | 56.3% | — |
| GSO | 88.2% | — |
| WeirdML | 92.9% | — |
| MirrorCode | 73.3% | — |
| ALE-Bench | 2,143 | — |
Agentic & Tool Use Not comparable
Claude Fable 5.1: 50.7 (#5), Step 5 Preview: —
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| APEX-Agents | 68.6% | — |
| Remote Labor Index | 17.9% | — |
| GDP.pdf | 29.6% | — |
| Vending-Bench 2 | 5,422 | — |
Reasoning Claude Fable 5.1 leads
Claude Fable 5.1: 76.7 (#7), Step 5 Preview: 40.0 (#57)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| CritPt | 31.1% | 20.9% |
| LMArena Hard Prompts | 1526 | 1465 |
| ARC-AGI-2 | 90% | — |
| NYT Connections (extended) | 90% | — |
| ARC-AGI-1 | 97.5% | — |
| Chess Puzzles | 47% | — |
| EBR-Bench | 57.1% | — |
| Mystery Game Puzzles | 58% | — |
| DTBench | 97.6% | — |
| LMCA | 65.5% | — |
| Epoch Capabilities Index | 164.7 | — |
Math Claude Fable 5.1 leads
Claude Fable 5.1: 89.6 (#4), Step 5 Preview: 46.1 (#72)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| ProofBench | 100% | 42% |
| LMArena Math | 1525 | 1470 |
| FrontierMath (Tiers 1-3) | 90.2% | — |
| FrontierMath Tier 4 | 87.8% | — |
| OTIS Mock AIME 2024-2025 | 100% | — |
| FrontierMath Erdős | 0% | — |
Knowledge Claude Fable 5.1 leads
Claude Fable 5.1: 69.6 (#6), Step 5 Preview: 41.2 (#112)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Expert | 1535 | 1470 |
| Humanity's Last Exam | 46.5% | — |
| SimpleQA Verified | 70.8% | — |
Multimodal Claude Fable 5.1 leads
Claude Fable 5.1: 53.9 (#4), Step 5 Preview: 41.0 (#41)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Vision | 1318 | 1267 |
| Blueprint-Bench 2 | 41.9% | — |
| Furniture Assembly | 70% | — |
| LMArena Document | 1513 | — |
Multilingual Claude Fable 5.1 leads
Claude Fable 5.1: 59.1 (#3), Step 5 Preview: 53.8 (#54)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Non-English | 1507 | 1432 |
| LMArena Chinese | 1586 | 1519 |
| LMArena Russian | 1521 | 1436 |
| LMArena Spanish | 1516 | 1439 |
| LMArena French | 1525 | — |
| LMArena German | 1500 | — |
| LMArena Japanese | 1543 | — |
| LMArena Korean | 1534 | — |
Instruction Following Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#6), Step 5 Preview: 76.0 (#50)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Instruction Following | 1517 | 1444 |
Long Context Claude Fable 5.1 leads
Claude Fable 5.1: 46.7 (#20), Step 5 Preview: 44.5 (#64)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Longer Query | 1522 | 1455 |
Writing & Preference Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#2), Step 5 Preview: 62.8 (#71)
| Benchmark | Claude Fable 5.1 | Step 5 Preview |
|---|---|---|
| LMArena Text | 1510 | 1442 |
| LMArena Creative Writing | 1507 | 1410 |
| LMArena Multi-Turn | 1492 | 1447 |
| EQ-Bench Creative Writing | 2162 | — |
Frequently asked questions
Is Claude Fable 5.1 better than Step 5 Preview?
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 47.9 on the Noometry Index. Step 5 Preview costs 14× 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 Step 5 Preview?
Step 5 Preview is cheaper. It lists at $1 per million input tokens and $2.70 per million output tokens; Claude Fable 5.1 lists at $10 and $50.
Is Claude Fable 5.1 or Step 5 Preview better for coding?
Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 51.8 in the Noometry coding category.
Which has the bigger context window?
Step 5 Preview does, with 1.02M tokens against 1M.
How many benchmarks do Claude Fable 5.1 and Step 5 Preview share?
18 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and Step 5 Preview has 18.