Side-by-side benchmark comparison across knowledge, coding, math, and reasoning.
GPT-OSS 20B has the cleaner overall profile here, landing at 34 versus 31. It is a real lead, but still close enough that category-level strengths matter more than the headline number.
GPT-5 nano is the reasoning model in the pair, while GPT-OSS 20B is not. That usually helps on harder chain-of-thought-heavy tests, but it can also mean more latency and more token spend in real use. GPT-5 nano gives you the larger context window at 400K, compared with 128K for GPT-OSS 20B.
Pick GPT-OSS 20B if you want the stronger benchmark profile. GPT-5 nano only becomes the better choice if mathematics is the priority or you need the larger 400K context window.
GPT-OSS 20B
28.2
GPT-5 nano
71.2
GPT-OSS 20B
33.6
GPT-5 nano
85.2
GPT-OSS 20B is ahead overall, 34 to 31. The biggest single separator in this matchup is AIME 2025, where the scores are 32 and 85.2.
GPT-5 nano has the edge for knowledge tasks in this comparison, averaging 71.2 versus 28.2. Inside this category, GPQA is the benchmark that creates the most daylight between them.
GPT-5 nano has the edge for math in this comparison, averaging 85.2 versus 33.6. Inside this category, AIME 2025 is the benchmark that creates the most daylight between them.
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