Anthropic Claude Opus 4.5 vs OpenAI gpt-oss-20b — side-by-side specs.
Anthropic Claude Opus 4.5 | OpenAI gpt-oss-20b | |
|---|---|---|
| Overview | ||
| Company | Anthropic | OpenAI |
| Release date | Nov 24 2025 | Aug 5 2025 |
| Model type | — | — |
| Open source | No | Yes |
| Specifications | ||
Parameters | — | — |
Context window | — | — |
| Benchmarks | ||
Coding SWE-Bench VerifiedReal coding tasks pulled from open-source projects — the AI has to find and fix actual bugs. A human-checked version of the original SWE-Bench. Higher is better. | 80.9% | — |
Science GPQA DiamondGraduate-level science questions in biology, physics, and chemistry — hard enough that subject-matter PhDs score around 65%. Higher is better. | 87% | — |
| Timeline | ||
| Release gap | gpt-oss-20b shipped 111 days before Claude Opus 4.5 | |
Claude Opus 4.5 and gpt-oss-20b don't publish scores on any of the same benchmarks, so there's no direct head-to-head comparison. gpt-oss-20b shipped 111 days before Claude Opus 4.5, so benchmark comparisons should account for the intervening progress.
gpt-oss-20b is an open-source / open-weight model; Claude Opus 4.5 is proprietary.
Direct benchmark comparisons are unavailable — Claude Opus 4.5 and gpt-oss-20b don't publish scores on any of the same benchmarks.