Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
o3-pro is clearly ahead on the aggregate, 71 to 66. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
o3-pro's sharpest advantage is in agentic, where it averages 70.4 against 60.2. The single biggest benchmark swing on the page is OSWorld-Verified, 68 to 54. Step 3.5 Flash does hit back in instruction following, so the answer changes if that is the part of the workload you care about most.
o3-pro 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 o3-pro.
Pick o3-pro if you want the stronger benchmark profile. Step 3.5 Flash only becomes the better choice if instruction following is the priority or you need the larger 256K context window.
o3-pro
70.4
Step 3.5 Flash
60.2
o3-pro
49.2
Step 3.5 Flash
47.1
o3-pro
74.1
Step 3.5 Flash
66.7
o3-pro
83.6
Step 3.5 Flash
78.3
o3-pro
67.1
Step 3.5 Flash
60.8
o3-pro
82
Step 3.5 Flash
87
o3-pro
81.1
Step 3.5 Flash
82.8
o3-pro
89
Step 3.5 Flash
84.5
o3-pro is ahead overall, 71 to 66. The biggest single separator in this matchup is OSWorld-Verified, where the scores are 68 and 54.
o3-pro has the edge for knowledge tasks in this comparison, averaging 67.1 versus 60.8. Inside this category, HLE is the benchmark that creates the most daylight between them.
o3-pro has the edge for coding in this comparison, averaging 49.2 versus 47.1. Inside this category, SWE-bench Pro is the benchmark that creates the most daylight between them.
o3-pro has the edge for math in this comparison, averaging 89 versus 84.5. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
o3-pro has the edge for reasoning in this comparison, averaging 83.6 versus 78.3. Inside this category, MRCRv2 is the benchmark that creates the most daylight between them.
o3-pro has the edge for agentic tasks in this comparison, averaging 70.4 versus 60.2. Inside this category, OSWorld-Verified is the benchmark that creates the most daylight between them.
o3-pro has the edge for multimodal and grounded tasks in this comparison, averaging 74.1 versus 66.7. Inside this category, OfficeQA Pro is the benchmark that creates the most daylight between them.
Step 3.5 Flash has the edge for instruction following in this comparison, averaging 87 versus 82. Inside this category, IFEval is the benchmark that creates the most daylight between them.
Step 3.5 Flash has the edge for multilingual tasks in this comparison, averaging 82.8 versus 81.1. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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