Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
GPT-5.2
79
Mellum2-12B-A2.5B-Thinking
59
Pick GPT-5.2 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority.
Coding
+5.2 difference
Knowledge
+34.8 difference
GPT-5.2
Mellum2-12B-A2.5B-Thinking
$1.75 / $14
N/A
73 t/s
N/A
130.34s
N/A
400K
128K
Pick GPT-5.2 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority.
GPT-5.2 is clearly ahead on the provisional aggregate, 79 to 59. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.2's sharpest advantage is in knowledge, where it averages 92.4 against 57.6. The single biggest benchmark swing on the page is GPQA, 92.4% to 57.6%. Mellum2-12B-A2.5B-Thinking does hit back in coding, so the answer changes if that is the part of the workload you care about most.
GPT-5.2 gives you the larger context window at 400K, compared with 128K for Mellum2-12B-A2.5B-Thinking.
GPT-5.2 is ahead on BenchLM's provisional leaderboard, 79 to 59. The biggest single separator in this matchup is GPQA, where the scores are 92.4% and 57.6%.
GPT-5.2 has the edge for knowledge tasks in this comparison, averaging 92.4 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 64.7. GPT-5.2 stays close enough that the answer can still flip depending on your workload.
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