Model comparison
GPT-5.5 Pro vs gpt-oss-20b
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 32.1 on the Noometry Index. gpt-oss-20b costs 1875× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.
Last verified . 7 shared benchmarks.
Summary
- They share 7 benchmarks with published results for both. GPT-5.5 Pro scores higher in 3 categories and gpt-oss-20b in 0 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where GPT-5.5 Pro leads 73.6 to 18.8.
- The biggest single-benchmark swing is Chess Puzzles: 64% for GPT-5.5 Pro and 4% for gpt-oss-20b.
- gpt-oss-20b is cheaper at $0.018 / $0.09 per million input/output tokens, against $30 / $180 for GPT-5.5 Pro.
- GPT-5.5 Pro accepts more context: 1.05M tokens versus 131K.
- gpt-oss-20b has downloadable open weights; the other is API-only.
Side by side
| GPT-5.5 Pro | gpt-oss-20b | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 64.3 | 32.1 |
| Released | 2026-04-23 | 2025-08-05 |
| Weights | Proprietary | Open |
| Context window | 1.05M | 131K |
| Max output | 128K | 16K |
| Input $ / M tokens | $30 | $0.018 |
| Output $ / M tokens | $180 | $0.09 |
| Results tracked | 14 | 34 |
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Category by category
Coding Not comparable
GPT-5.5 Pro: —, gpt-oss-20b: 37.1 (#185)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| SciCode | — | 34.4% |
| WeirdML | — | 40.9% |
| LMArena Coding | — | 1307 |
| ALE-Bench | — | 566.05 |
Agentic & Tool Use Not comparable
GPT-5.5 Pro: —, gpt-oss-20b: 9.2 (#146)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| Terminal-Bench | — | 3.4% |
Reasoning GPT-5.5 Pro leads
GPT-5.5 Pro: 73.6 (#7), gpt-oss-20b: 18.8 (#251)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| CritPt | 30.6% | 1.4% |
| Chess Puzzles | 64% | 4% |
| DTBench | 96% | 68% |
| LMCA | 53.9% | 14.5% |
| Epoch Capabilities Index | 162.45 | 137.81 |
| ARC-AGI-2 | 84.6% | — |
| SimpleBench | 76.9% | — |
| Kagi LLM Benchmark | — | 53.2% |
| ARC-AGI-1 | 96.5% | — |
| LMArena Hard Prompts | — | 1274 |
Math GPT-5.5 Pro leads
GPT-5.5 Pro: 83.8 (#8), gpt-oss-20b: 37.6 (#93)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 100% | 65.3% |
| FrontierMath (Tiers 1-3) | 87.7% | — |
| FrontierMath Tier 4 | 78% | — |
| Omni-MATH | — | 56.5% |
| LMArena Math | — | 1317 |
| FrontierMath (Feb 2025 set) | 52.4% | — |
| FrontierMath Tier 4 (v1) | 39.6% | — |
Knowledge GPT-5.5 Pro leads
GPT-5.5 Pro: 64.2 (#17), gpt-oss-20b: 34.6 (#186)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| GPQA Diamond | 93.9% | 60.8% |
| MMLU-Pro | — | 74% |
| GPQA (HELM) | — | 59.4% |
| LMArena Expert | — | 1258 |
Multilingual Not comparable
GPT-5.5 Pro: —, gpt-oss-20b: 42.4 (#192)
| Benchmark | GPT-5.5 Pro | 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
GPT-5.5 Pro: —, gpt-oss-20b: 62.0 (#235)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| IFEval | — | 73.2% |
| LMArena Instruction Following | — | 1236 |
Long Context Not comparable
GPT-5.5 Pro: —, gpt-oss-20b: 37.9 (#203)
| Benchmark | GPT-5.5 Pro | gpt-oss-20b |
|---|---|---|
| LMArena Longer Query | — | 1251 |
Writing & Preference Not comparable
GPT-5.5 Pro: —, gpt-oss-20b: 35.8 (#260)
| Benchmark | GPT-5.5 Pro | 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 GPT-5.5 Pro better than gpt-oss-20b?
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 32.1 on the Noometry Index. gpt-oss-20b costs 1875× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.
Which is cheaper, GPT-5.5 Pro 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; GPT-5.5 Pro lists at $30 and $180.
Which has the bigger context window?
GPT-5.5 Pro does, with 1.05M tokens against 131K.
How many benchmarks do GPT-5.5 Pro and gpt-oss-20b share?
7 benchmarks have published results for both models. GPT-5.5 Pro has 14 scored results on Noometry and gpt-oss-20b has 34.