Model comparison
Claude Fable 5.1 vs gpt-oss-20b
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 32.5 on the Noometry Index. gpt-oss-20b costs 556× less per token, which makes it the better buy when Claude Fable 5.1's lead doesn't matter for your workload.
Last verified . 26 shared benchmarks.
Summary
- They share 26 benchmarks with published results for both. Claude Fable 5.1 scores higher in 9 categories and gpt-oss-20b in 0 categories; 9 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where Claude Fable 5.1 leads 76.7 to 19.3.
- The biggest single-benchmark swing is WeirdML: 92.9% for Claude Fable 5.1 and 40.9% for gpt-oss-20b.
- gpt-oss-20b is cheaper at $0.018 / $0.09 per million input/output tokens, against $10 / $50 for Claude Fable 5.1.
- Claude Fable 5.1 accepts more context: 1M tokens versus 131K.
- gpt-oss-20b has downloadable open weights; the other is API-only.
Side by side
| Claude Fable 5.1 | gpt-oss-20b | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Noometry Index | 69.0 | 32.5 |
| Released | 2026-09-01 | 2025-08-05 |
| Weights | Proprietary | Open |
| Context window | 1M | 131K |
| Max output | 128K | 16K |
| Input $ / M tokens | $10 | $0.018 |
| Output $ / M tokens | $50 | $0.09 |
| Results tracked | 52 | 34 |
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Category by category
Coding Claude Fable 5.1 leads
Claude Fable 5.1: 74.7 (#1), gpt-oss-20b: 37.6 (#192)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| SciCode | 63.1% | 34.4% |
| WeirdML | 92.9% | 40.9% |
| LMArena Coding | 1528 | 1306 |
| ALE-Bench | 2,143 | 566.05 |
| FrontierCode | 50.9% | — |
| CursorBench | 51.8% | — |
| LMArena WebDev | 1744 | — |
| FrontierSWE | 56.3% | — |
| GSO | 88.2% | — |
| MirrorCode | 73.3% | — |
Agentic & Tool Use Claude Fable 5.1 leads
Claude Fable 5.1: 50.7 (#5), gpt-oss-20b: 9.3 (#154)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| Terminal-Bench | — | 3.4% |
| 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), gpt-oss-20b: 19.3 (#261)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| CritPt | 31.1% | 1.4% |
| Chess Puzzles | 47% | 4% |
| LMArena Hard Prompts | 1526 | 1274 |
| DTBench | 97.6% | 68% |
| LMCA | 65.5% | 14.5% |
| Epoch Capabilities Index | 164.7 | 137.82 |
| ARC-AGI-2 | 90% | — |
| Kagi LLM Benchmark | — | 53.2% |
| NYT Connections (extended) | 90% | — |
| ARC-AGI-1 | 97.5% | — |
| EBR-Bench | 57.1% | — |
| Mystery Game Puzzles | 58% | — |
Math Claude Fable 5.1 leads
Claude Fable 5.1: 89.6 (#4), gpt-oss-20b: 39.4 (#103)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 100% | 65.3% |
| LMArena Math | 1525 | 1317 |
| FrontierMath (Tiers 1-3) | 90.2% | — |
| FrontierMath Tier 4 | 87.8% | — |
| ProofBench | 100% | — |
| Omni-MATH | — | 56.5% |
| FrontierMath Erdős | 0% | — |
Knowledge Claude Fable 5.1 leads
Claude Fable 5.1: 69.6 (#6), gpt-oss-20b: 34.6 (#195)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Expert | 1535 | 1258 |
| GPQA Diamond | — | 60.8% |
| Humanity's Last Exam | 46.5% | — |
| SimpleQA Verified | 70.8% | — |
| MMLU-Pro | — | 74% |
| GPQA (HELM) | — | 59.4% |
Multimodal Not comparable
Claude Fable 5.1: 53.9 (#4), gpt-oss-20b: —
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Vision | 1318 | — |
| Blueprint-Bench 2 | 41.9% | — |
| Furniture Assembly | 70% | — |
| LMArena Document | 1513 | — |
Multilingual Claude Fable 5.1 leads
Claude Fable 5.1: 59.1 (#3), gpt-oss-20b: 42.2 (#197)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Non-English | 1507 | 1268 |
| LMArena Chinese | 1586 | 1314 |
| LMArena German | 1500 | 1255 |
| LMArena Japanese | 1543 | 1244 |
| LMArena Korean | 1534 | 1236 |
| LMArena Russian | 1521 | 1278 |
| LMArena Spanish | 1516 | 1267 |
| LMArena French | 1525 | — |
Instruction Following Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#6), gpt-oss-20b: 61.8 (#240)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Instruction Following | 1517 | 1236 |
| IFEval | — | 73.2% |
Long Context Claude Fable 5.1 leads
Claude Fable 5.1: 46.7 (#20), gpt-oss-20b: 37.9 (#209)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Longer Query | 1522 | 1250 |
Writing & Preference Claude Fable 5.1 leads
Claude Fable 5.1: 79.2 (#2), gpt-oss-20b: 35.5 (#265)
| Benchmark | Claude Fable 5.1 | gpt-oss-20b |
|---|---|---|
| LMArena Text | 1510 | 1287 |
| LMArena Creative Writing | 1507 | 1201 |
| EQ-Bench Creative Writing | 2162 | 666 |
| LMArena Multi-Turn | 1492 | 1268 |
| WildBench | — | 73.7% |
Frequently asked questions
Is Claude Fable 5.1 better than gpt-oss-20b?
Claude Fable 5.1 is the stronger model overall, scoring 69.0 to 32.5 on the Noometry Index. gpt-oss-20b costs 556× 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 gpt-oss-20b?
gpt-oss-20b is cheaper. It lists at $0.018 per million input tokens and $0.09 per million output tokens; Claude Fable 5.1 lists at $10 and $50.
Is Claude Fable 5.1 or gpt-oss-20b better for coding?
Claude Fable 5.1 scores higher on coding benchmarks: 74.7 versus 37.6 in the Noometry coding category.
Which has the bigger context window?
Claude Fable 5.1 does, with 1M tokens against 131K.
How many benchmarks do Claude Fable 5.1 and gpt-oss-20b share?
26 benchmarks have published results for both models. Claude Fable 5.1 has 52 scored results on Noometry and gpt-oss-20b has 34.