Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
GPT-5.3 Instant is clearly ahead on the aggregate, 87 to 35. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.3 Instant's sharpest advantage is in coding, where it averages 78.7 against 14.5. The single biggest benchmark swing on the page is MMLU, 99 to 31.
GPT-5.3 Instant 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.
Pick GPT-5.3 Instant if you want the stronger benchmark profile. GPT-OSS 20B only becomes the better choice if you would rather avoid the extra latency and token burn of a reasoning model.
GPT-5.3 Instant
82.9
GPT-OSS 20B
35.4
GPT-5.3 Instant
78.7
GPT-OSS 20B
14.5
GPT-5.3 Instant
95
GPT-OSS 20B
36
GPT-5.3 Instant
94.2
GPT-OSS 20B
40.4
GPT-5.3 Instant
80.8
GPT-OSS 20B
29
GPT-5.3 Instant
96
GPT-OSS 20B
67
GPT-5.3 Instant
93.4
GPT-OSS 20B
59.7
GPT-5.3 Instant
97.2
GPT-OSS 20B
43.1
GPT-5.3 Instant is ahead overall, 87 to 35. The biggest single separator in this matchup is MMLU, where the scores are 99 and 31.
GPT-5.3 Instant has the edge for knowledge tasks in this comparison, averaging 80.8 versus 29. Inside this category, MMLU is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for coding in this comparison, averaging 78.7 versus 14.5. Inside this category, HumanEval is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for math in this comparison, averaging 97.2 versus 43.1. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for reasoning in this comparison, averaging 94.2 versus 40.4. Inside this category, SimpleQA is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for agentic tasks in this comparison, averaging 82.9 versus 35.4. Inside this category, Terminal-Bench 2.0 is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for multimodal and grounded tasks in this comparison, averaging 95 versus 36. Inside this category, MMMU-Pro is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for instruction following in this comparison, averaging 96 versus 67. Inside this category, IFEval is the benchmark that creates the most daylight between them.
GPT-5.3 Instant has the edge for multilingual tasks in this comparison, averaging 93.4 versus 59.7. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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