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 65. 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 41.1. The single biggest benchmark swing on the page is SWE-bench Pro, 83 to 43.
GPT-5.3 Instant is also the more expensive model on tokens at $1.75 input / $14.00 output per 1M tokens, versus $0.25 input / $0.75 output per 1M tokens for Mercury 2. That is roughly 18.7x on output cost alone.
Pick GPT-5.3 Instant if you want the stronger benchmark profile. Mercury 2 only becomes the better choice if you want the cheaper token bill.
GPT-5.3 Instant
82.9
Mercury 2
63.7
GPT-5.3 Instant
78.7
Mercury 2
41.1
GPT-5.3 Instant
95
Mercury 2
68.3
GPT-5.3 Instant
94.2
Mercury 2
80.1
GPT-5.3 Instant
80.8
Mercury 2
57.2
GPT-5.3 Instant
96
Mercury 2
84
GPT-5.3 Instant
93.4
Mercury 2
79.7
GPT-5.3 Instant
97.2
Mercury 2
80.9
GPT-5.3 Instant is ahead overall, 87 to 65. The biggest single separator in this matchup is SWE-bench Pro, where the scores are 83 and 43.
GPT-5.3 Instant has the edge for knowledge tasks in this comparison, averaging 80.8 versus 57.2. Inside this category, HLE 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 41.1. Inside this category, SWE-bench Pro 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 80.9. 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 80.1. Inside this category, MRCRv2 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 63.7. 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 68.3. 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 84. 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 79.7. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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