Side-by-side benchmark comparison across agentic, coding, multimodal, knowledge, reasoning, and math workflows.
Step 3.5 Flash finishes one point ahead overall, 66 to 65. That is enough to call, but not enough to treat as a blowout. This matchup comes down to a few meaningful edges rather than one model dominating the board.
Step 3.5 Flash's sharpest advantage is in coding, where it averages 47.1 against 41.1. The single biggest benchmark swing on the page is OSWorld-Verified, 54 to 62. Mercury 2 does hit back in agentic, so the answer changes if that is the part of the workload you care about most.
Mercury 2 is also the more expensive model on tokens at $0.25 input / $0.75 output per 1M tokens, versus $0.10 input / $0.30 output per 1M tokens for Step 3.5 Flash. That is roughly 2.5x on output cost alone. Mercury 2 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 128K for Mercury 2.
Pick Step 3.5 Flash if you want the stronger benchmark profile. Mercury 2 only becomes the better choice if agentic is the priority or you want the stronger reasoning-first profile.
Step 3.5 Flash
60.2
Mercury 2
63.7
Step 3.5 Flash
47.1
Mercury 2
41.1
Step 3.5 Flash
66.7
Mercury 2
68.3
Step 3.5 Flash
78.3
Mercury 2
80.1
Step 3.5 Flash
60.8
Mercury 2
57.2
Step 3.5 Flash
87
Mercury 2
84
Step 3.5 Flash
82.8
Mercury 2
79.7
Step 3.5 Flash
84.5
Mercury 2
80.9
Step 3.5 Flash is ahead overall, 66 to 65. The biggest single separator in this matchup is OSWorld-Verified, where the scores are 54 and 62.
Step 3.5 Flash has the edge for knowledge tasks in this comparison, averaging 60.8 versus 57.2. Inside this category, MMLU is the benchmark that creates the most daylight between them.
Step 3.5 Flash has the edge for coding in this comparison, averaging 47.1 versus 41.1. Inside this category, LiveCodeBench is the benchmark that creates the most daylight between them.
Step 3.5 Flash has the edge for math in this comparison, averaging 84.5 versus 80.9. Inside this category, AIME 2023 is the benchmark that creates the most daylight between them.
Mercury 2 has the edge for reasoning in this comparison, averaging 80.1 versus 78.3. Inside this category, BBH is the benchmark that creates the most daylight between them.
Mercury 2 has the edge for agentic tasks in this comparison, averaging 63.7 versus 60.2. Inside this category, OSWorld-Verified is the benchmark that creates the most daylight between them.
Mercury 2 has the edge for multimodal and grounded tasks in this comparison, averaging 68.3 versus 66.7. Inside this category, MMMU-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 84. 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 79.7. Inside this category, MGSM is the benchmark that creates the most daylight between them.
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