Head-to-head comparison across 3benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Mellum2-12B-A2.5B-Thinking
59
o3-mini
55
Pick Mellum2-12B-A2.5B-Thinking if you want the stronger benchmark profile. o3-mini only becomes the better choice if knowledge is the priority or you need the larger 200K context window.
Coding
+20.6 difference
Knowledge
+19.6 difference
Inst. Following
+17.4 difference
Mellum2-12B-A2.5B-Thinking
o3-mini
N/A
$1.1 / $4.4
N/A
160 t/s
N/A
7.12s
128K
200K
Pick Mellum2-12B-A2.5B-Thinking if you want the stronger benchmark profile. o3-mini only becomes the better choice if knowledge is the priority or you need the larger 200K context window.
Mellum2-12B-A2.5B-Thinking is clearly ahead on the provisional aggregate, 59 to 55. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Mellum2-12B-A2.5B-Thinking's sharpest advantage is in coding, where it averages 69.9 against 49.3. The single biggest benchmark swing on the page is GPQA, 57.6% to 77.2%. o3-mini does hit back in knowledge, so the answer changes if that is the part of the workload you care about most.
o3-mini gives you the larger context window at 200K, compared with 128K for Mellum2-12B-A2.5B-Thinking.
Mellum2-12B-A2.5B-Thinking is ahead on BenchLM's provisional leaderboard, 59 to 55. The biggest single separator in this matchup is GPQA, where the scores are 57.6% and 77.2%.
o3-mini has the edge for knowledge tasks in this comparison, averaging 77.2 versus 57.6. Inside this category, GPQA is the benchmark that creates the most daylight between them.
Mellum2-12B-A2.5B-Thinking has the edge for coding in this comparison, averaging 69.9 versus 49.3. o3-mini stays close enough that the answer can still flip depending on your workload.
o3-mini has the edge for instruction following in this comparison, averaging 93.9 versus 76.5. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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