Model comparison
GPT-5.5 Pro vs gpt-oss-120b
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 36.3 on the Noometry Index. gpt-oss-120b costs 961× less per token, which makes it the better buy when GPT-5.5 Pro's lead doesn't matter for your workload.
Last verified . 8 shared benchmarks.
Summary
- They share 8 benchmarks with published results for both. GPT-5.5 Pro scores higher in 3 categories and gpt-oss-120b in 0 categories; 3 gaps are clear of the uncertainty.
- The widest gap is in reasoning, where GPT-5.5 Pro leads 73.3 to 20.0.
- The biggest single-benchmark swing is SimpleBench: 76.9% for GPT-5.5 Pro and 22.1% for gpt-oss-120b.
- gpt-oss-120b is cheaper at $0.037 / $0.17 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-120b has downloadable open weights; the other is API-only.
Side by side
| GPT-5.5 Pro | gpt-oss-120b | |
|---|---|---|
| Provider | OpenAI | OpenAI |
| Noometry Index | 64.3 | 36.3 |
| Released | 2026-04-23 | 2025-08-05 |
| Weights | Proprietary | Open |
| Context window | 1.05M | 131K |
| Max output | 128K | 41K |
| Input $ / M tokens | $30 | $0.037 |
| Output $ / M tokens | $180 | $0.17 |
| Results tracked | 14 | 48 |
Sponsored placements are available on pages like this one. Advertise on Noometry
Category by category
Coding Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 33.5 (#256)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| SWE-bench Verified (bash only) | — | 26% |
| Aider Polyglot | — | 41.8% |
| SciCode | — | 36% |
| WeirdML | — | 48.2% |
| LMArena Coding | — | 1380 |
| ALE-Bench | — | 575.62 |
| AlgoTune | — | 1.41 |
Agentic & Tool Use Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 12.2 (#153)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| Terminal-Bench | — | 18.7% |
| APEX-Agents | — | 4.4% |
| METR Time Horizons | — | 56.6% |
| Vending-Bench 2 | — | -21.53 |
Reasoning GPT-5.5 Pro leads
GPT-5.5 Pro: 73.3 (#10), gpt-oss-120b: 20.0 (#245)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| SimpleBench | 76.9% | 22.1% |
| CritPt | 30.6% | 1.1% |
| Chess Puzzles | 64% | 20% |
| DTBench | 96% | 76.3% |
| LMCA | 53.9% | 22.1% |
| Epoch Capabilities Index | 162.07 | 139.93 |
| ARC-AGI-2 | 84.6% | — |
| Kagi LLM Benchmark | — | 58.6% |
| ARC-AGI-1 | 96.5% | — |
| LMArena Hard Prompts | — | 1364 |
| Mystery Game Puzzles | — | 2% |
| Surface Evolver Bench | — | 25% |
Math GPT-5.5 Pro leads
GPT-5.5 Pro: 84.0 (#10), gpt-oss-120b: 52.5 (#50)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| OTIS Mock AIME 2024-2025 | 100% | 88.9% |
| FrontierMath (Tiers 1-3) | 87.7% | — |
| FrontierMath Tier 4 | 78% | — |
| Omni-MATH | — | 68.8% |
| LMArena Math | — | 1389 |
| FrontierMath (Feb 2025 set) | 52.4% | — |
| FrontierMath Tier 4 (v1) | 39.6% | — |
Knowledge GPT-5.5 Pro leads
GPT-5.5 Pro: 64.1 (#19), gpt-oss-120b: 42.4 (#96)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| GPQA Diamond | 93.9% | 75.8% |
| MMLU-Pro | — | 79.5% |
| Confabulations | — | 15.7% |
| Vectara Hallucination Rate | — | 14.2% |
| GPQA (HELM) | — | 68.4% |
| LMArena Expert | — | 1356 |
Multilingual Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 48.0 (#147)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| LMArena Non-English | — | 1351 |
| LMArena Chinese | — | 1385 |
| LMArena French | — | 1369 |
| LMArena German | — | 1353 |
| LMArena Japanese | — | 1331 |
| LMArena Korean | — | 1282 |
| LMArena Russian | — | 1343 |
| LMArena Spanish | — | 1389 |
Instruction Following Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 69.3 (#173)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| IFEval | — | 83.6% |
| LMArena Instruction Following | — | 1318 |
Long Context Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 31.4 (#278)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| Fiction.LiveBench | — | 44.4% |
| LMArena Longer Query | — | 1319 |
Writing & Preference Not comparable
GPT-5.5 Pro: —, gpt-oss-120b: 46.5 (#217)
| Benchmark | GPT-5.5 Pro | gpt-oss-120b |
|---|---|---|
| LMArena Text | — | 1365 |
| LMArena Creative Writing | — | 1275 |
| Short-Story Creative Writing | — | 77.1% |
| EQ-Bench Creative Writing | — | 961 |
| WildBench | — | 84.5% |
| LMArena Multi-Turn | — | 1340 |
Frequently asked questions
Is GPT-5.5 Pro better than gpt-oss-120b?
GPT-5.5 Pro is the stronger model overall, scoring 64.3 to 36.3 on the Noometry Index. gpt-oss-120b costs 961× 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-120b?
gpt-oss-120b is cheaper. It lists at $0.037 per million input tokens and $0.17 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-120b share?
8 benchmarks have published results for both models. GPT-5.5 Pro has 14 scored results on Noometry and gpt-oss-120b has 48.