Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
GPT-5.1 is clearly ahead on the aggregate, 80 to 66. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.1's sharpest advantage is in multimodal & grounded, where it averages 91.8 against 66.7. The single biggest benchmark swing on the page is MMMU-Pro, 94 to 64.
GPT-5.1 is also the more expensive model on tokens at $1.50 input / $6.00 output per 1M tokens, versus $0.10 input / $0.30 output per 1M tokens for Step 3.5 Flash. That is roughly 20.0x on output cost alone. GPT-5.1 is the reasoning model in the pair, while Step 3.5 Flash 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. Step 3.5 Flash gives you the larger context window at 256K, compared with 200K for GPT-5.1.
Pick GPT-5.1 if you want the stronger benchmark profile. Step 3.5 Flash only becomes the better choice if you want the cheaper token bill or you need the larger 256K context window.
GPT-5.1
75.8
Step 3.5 Flash
60.2
GPT-5.1
66.2
Step 3.5 Flash
47.1
GPT-5.1
91.8
Step 3.5 Flash
66.7
GPT-5.1
88.4
Step 3.5 Flash
78.3
GPT-5.1
72.5
Step 3.5 Flash
60.8
GPT-5.1
89
Step 3.5 Flash
87
GPT-5.1
87.7
Step 3.5 Flash
82.8
GPT-5.1
95.4
Step 3.5 Flash
84.5
GPT-5.1 is ahead overall, 80 to 66. The biggest single separator in this matchup is MMMU-Pro, where the scores are 94 and 64.
GPT-5.1 has the edge for knowledge tasks in this comparison, averaging 72.5 versus 60.8. Inside this category, HLE is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for coding in this comparison, averaging 66.2 versus 47.1. Inside this category, SWE-bench Pro is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for math in this comparison, averaging 95.4 versus 84.5. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for reasoning in this comparison, averaging 88.4 versus 78.3. Inside this category, SimpleQA is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for agentic tasks in this comparison, averaging 75.8 versus 60.2. Inside this category, OSWorld-Verified is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for multimodal and grounded tasks in this comparison, averaging 91.8 versus 66.7. Inside this category, MMMU-Pro is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for instruction following in this comparison, averaging 89 versus 87. Inside this category, IFEval is the benchmark that creates the most daylight between them.
GPT-5.1 has the edge for multilingual tasks in this comparison, averaging 87.7 versus 82.8. Inside this category, MMLU-ProX is the benchmark that creates the most daylight between them.
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