Side-by-side benchmark comparison across knowledge, coding, math, and reasoning.
o3 is clearly ahead on the aggregate, 76 to 31. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
o3's sharpest advantage is in knowledge, where it averages 73.3 against 71.2. The single biggest benchmark swing on the page is GPQA, 87 to 71.2.
o3 is also the more expensive model on tokens at $10.00 input / $40.00 output per 1M tokens, versus $0.05 input / $0.40 output per 1M tokens for GPT-5 nano. That is roughly 100.0x on output cost alone. GPT-5 nano gives you the larger context window at 400K, compared with 200K for o3.
Pick o3 if you want the stronger benchmark profile. GPT-5 nano only becomes the better choice if you want the cheaper token bill or you need the larger 400K context window.
o3
73.3
GPT-5 nano
71.2
o3
87.1
GPT-5 nano
85.2
o3 is ahead overall, 76 to 31. The biggest single separator in this matchup is GPQA, where the scores are 87 and 71.2.
o3 has the edge for knowledge tasks in this comparison, averaging 73.3 versus 71.2. Inside this category, GPQA is the benchmark that creates the most daylight between them.
o3 has the edge for math in this comparison, averaging 87.1 versus 85.2. Inside this category, AIME 2025 is the benchmark that creates the most daylight between them.
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