Model comparison
Claude Sonnet 5.5 vs gpt-oss-20b
Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 32.1 on the Noometry Index. gpt-oss-20b costs 111× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Last verified . 5 shared benchmarks.
Summary
- They share 5 benchmarks with published results for both. Claude Sonnet 5.5 scores higher in 5 categories and gpt-oss-20b in 0 categories; 5 gaps are clear of the uncertainty.
- The widest gap is in math, where Claude Sonnet 5.5 leads 88.7 to 37.6.
- The biggest single-benchmark swing is GPQA Diamond: 95.6% for Claude Sonnet 5.5 and 60.8% for gpt-oss-20b.
- gpt-oss-20b is cheaper at $0.018 / $0.09 per million input/output tokens, against $2 / $10 for Claude Sonnet 5.5.
- Claude Sonnet 5.5 accepts more context: 1M tokens versus 131K.
- gpt-oss-20b has downloadable open weights; the other is API-only.
Side by side
| Claude Sonnet 5.5 | gpt-oss-20b | |
|---|---|---|
| Provider | Anthropic | OpenAI |
| Noometry Index | 60.5 | 32.1 |
| Released | 2026-09-28 | 2025-08-05 |
| Weights | Proprietary | Open |
| Context window | 1M | 131K |
| Max output | 128K | 16K |
| Input $ / M tokens | $2 | $0.018 |
| Output $ / M tokens | $10 | $0.09 |
| Results tracked | 16 | 34 |
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Category by category
Coding Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 65.5 (#6), gpt-oss-20b: 37.1 (#185)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| SciCode | 61% | 34.4% |
| ALE-Bench | 1,819 | 566.05 |
| FrontierCode | 52.1% | — |
| CursorBench | 55.5% | — |
| LMArena WebDev | 1699 | — |
| FrontierSWE | 61.9% | — |
| WeirdML | — | 40.9% |
| LMArena Coding | — | 1307 |
Agentic & Tool Use Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 44.9 (#14), gpt-oss-20b: 9.2 (#146)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| Terminal-Bench | — | 3.4% |
| APEX-Agents | 75.5% | — |
Reasoning Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 52.4 (#29), gpt-oss-20b: 18.8 (#251)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| CritPt | 31.4% | 1.4% |
| Kagi LLM Benchmark | — | 53.2% |
| Chess Puzzles | — | 4% |
| LMArena Hard Prompts | — | 1274 |
| Mystery Game Puzzles | 65% | — |
| DTBench | — | 68% |
| LMCA | — | 14.5% |
| Epoch Capabilities Index | — | 137.81 |
Math Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 88.7 (#4), gpt-oss-20b: 37.6 (#93)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 100% | 65.3% |
| FrontierMath (Tiers 1-3) | 88.8% | — |
| FrontierMath Tier 4 | 80.5% | — |
| ProofBench | 100% | — |
| Omni-MATH | — | 56.5% |
| LMArena Math | — | 1317 |
Knowledge Claude Sonnet 5.5 leads
Claude Sonnet 5.5: 66.0 (#11), gpt-oss-20b: 34.6 (#186)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| GPQA Diamond | 95.6% | 60.8% |
| SimpleQA Verified | 46.5% | — |
| MMLU-Pro | — | 74% |
| GPQA (HELM) | — | 59.4% |
| LMArena Expert | — | 1258 |
Multimodal Not comparable
Claude Sonnet 5.5: 53.2 (#5), gpt-oss-20b: —
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| Furniture Assembly | 75% | — |
Multilingual Not comparable
Claude Sonnet 5.5: —, gpt-oss-20b: 42.4 (#192)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| LMArena Non-English | — | 1269 |
| LMArena Chinese | — | 1311 |
| LMArena German | — | 1249 |
| LMArena Japanese | — | 1245 |
| LMArena Korean | — | 1239 |
| LMArena Russian | — | 1279 |
| LMArena Spanish | — | 1267 |
Instruction Following Not comparable
Claude Sonnet 5.5: —, gpt-oss-20b: 62.0 (#235)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| IFEval | — | 73.2% |
| LMArena Instruction Following | — | 1236 |
Long Context Not comparable
Claude Sonnet 5.5: —, gpt-oss-20b: 37.9 (#203)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| LMArena Longer Query | — | 1251 |
Writing & Preference Not comparable
Claude Sonnet 5.5: —, gpt-oss-20b: 35.8 (#260)
| Benchmark | Claude Sonnet 5.5 | gpt-oss-20b |
|---|---|---|
| LMArena Text | — | 1288 |
| LMArena Creative Writing | — | 1201 |
| EQ-Bench Creative Writing | — | 666 |
| WildBench | — | 73.7% |
| LMArena Multi-Turn | — | 1268 |
Frequently asked questions
Is Claude Sonnet 5.5 better than gpt-oss-20b?
Claude Sonnet 5.5 is the stronger model overall, scoring 60.5 to 32.1 on the Noometry Index. gpt-oss-20b costs 111× less per token, which makes it the better buy when Claude Sonnet 5.5's lead doesn't matter for your workload.
Which is cheaper, Claude Sonnet 5.5 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 Sonnet 5.5 lists at $2 and $10.
Is Claude Sonnet 5.5 or gpt-oss-20b better for coding?
Claude Sonnet 5.5 scores higher on coding benchmarks: 65.5 versus 37.1 in the Noometry coding category.
Which has the bigger context window?
Claude Sonnet 5.5 does, with 1M tokens against 131K.
How many benchmarks do Claude Sonnet 5.5 and gpt-oss-20b share?
5 benchmarks have published results for both models. Claude Sonnet 5.5 has 16 scored results on Noometry and gpt-oss-20b has 34.