Side-by-side benchmark comparison across knowledge, coding, math, and reasoning.
GPT-OSS 20B is clearly ahead on the aggregate, 34 to 23. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-OSS 20B's sharpest advantage is in mathematics, where it averages 33.6 against 9.8. The single biggest benchmark swing on the page is MMLU, 31 to 80.1. GPT-4.1 nano does hit back in knowledge, so the answer changes if that is the part of the workload you care about most.
GPT-4.1 nano gives you the larger context window at 1M, compared with 128K for GPT-OSS 20B.
Pick GPT-OSS 20B if you want the stronger benchmark profile. GPT-4.1 nano only becomes the better choice if knowledge is the priority or you need the larger 1M context window.
GPT-OSS 20B
28.2
GPT-4.1 nano
65.2
GPT-OSS 20B
33.6
GPT-4.1 nano
9.8
GPT-OSS 20B
67
GPT-4.1 nano
83.2
GPT-OSS 20B is ahead overall, 34 to 23. The biggest single separator in this matchup is MMLU, where the scores are 31 and 80.1.
GPT-4.1 nano has the edge for knowledge tasks in this comparison, averaging 65.2 versus 28.2. Inside this category, MMLU is the benchmark that creates the most daylight between them.
GPT-OSS 20B has the edge for math in this comparison, averaging 33.6 versus 9.8. Inside this category, AIME 2024 is the benchmark that creates the most daylight between them.
GPT-4.1 nano has the edge for instruction following in this comparison, averaging 83.2 versus 67. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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