Side-by-side benchmark comparison across knowledge, coding, math, and reasoning.
GPT-5.3 Codex is clearly ahead on the aggregate, 92 to 56. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.3 Codex's sharpest advantage is in coding, where it averages 88.3 against 49.3. The single biggest benchmark swing on the page is SWE-bench Verified, 85 to 49.3. o3-mini does hit back in instruction following, so the answer changes if that is the part of the workload you care about most.
GPT-5.3 Codex is also the more expensive model on tokens at $2.50 input / $10.00 output per 1M tokens, versus $1.10 input / $4.40 output per 1M tokens for o3-mini. That is roughly 2.3x on output cost alone. GPT-5.3 Codex gives you the larger context window at 400K, compared with 200K for o3-mini.
Pick GPT-5.3 Codex if you want the stronger benchmark profile. o3-mini only becomes the better choice if instruction following is the priority or you want the cheaper token bill.
GPT-5.3 Codex
86.3
o3-mini
82.1
GPT-5.3 Codex
88.3
o3-mini
49.3
GPT-5.3 Codex
97.4
o3-mini
87.3
GPT-5.3 Codex
93
o3-mini
93.9
GPT-5.3 Codex is ahead overall, 92 to 56. The biggest single separator in this matchup is SWE-bench Verified, where the scores are 85 and 49.3.
GPT-5.3 Codex has the edge for knowledge tasks in this comparison, averaging 86.3 versus 82.1. Inside this category, GPQA is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for coding in this comparison, averaging 88.3 versus 49.3. Inside this category, SWE-bench Verified is the benchmark that creates the most daylight between them.
GPT-5.3 Codex has the edge for math in this comparison, averaging 97.4 versus 87.3. Inside this category, AIME 2024 is the benchmark that creates the most daylight between them.
o3-mini has the edge for instruction following in this comparison, averaging 93.9 versus 93. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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