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 76. 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 57.5. The single biggest benchmark swing on the page is SWE-bench Pro, 83 to 60.
Claude Sonnet 4.5 is also the more expensive model on tokens at $3.00 input / $15.00 output per 1M tokens, versus $1.75 input / $14.00 output per 1M tokens for GPT-5.3 Instant. GPT-5.3 Instant is the reasoning model in the pair, while Claude Sonnet 4.5 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. Claude Sonnet 4.5 gives you the larger context window at 200K, compared with 128K for GPT-5.3 Instant.
Pick GPT-5.3 Instant if you want the stronger benchmark profile. Claude Sonnet 4.5 only becomes the better choice if you need the larger 200K context window or you would rather avoid the extra latency and token burn of a reasoning model.
GPT-5.3 Instant
82.9
Claude Sonnet 4.5
70.3
GPT-5.3 Instant
78.7
Claude Sonnet 4.5
57.5
GPT-5.3 Instant
95
Claude Sonnet 4.5
91.4
GPT-5.3 Instant
94.2
Claude Sonnet 4.5
86
GPT-5.3 Instant
80.8
Claude Sonnet 4.5
70.7
GPT-5.3 Instant
96
Claude Sonnet 4.5
90
GPT-5.3 Instant
93.4
Claude Sonnet 4.5
88.4
GPT-5.3 Instant
97.2
Claude Sonnet 4.5
92.4
GPT-5.3 Instant is ahead overall, 87 to 76. The biggest single separator in this matchup is SWE-bench Pro, where the scores are 83 and 60.
GPT-5.3 Instant has the edge for knowledge tasks in this comparison, averaging 80.8 versus 70.7. 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 57.5. 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 92.4. Inside this category, MATH-500 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 86. 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 70.3. 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 91.4. Inside this category, OfficeQA 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 90. 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 88.4. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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