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-Instruct
27
Pick GPT-5.2 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Instruct only becomes the better choice if you would rather avoid the extra latency and token burn of a reasoning model.
Coding
+27.5 difference
Knowledge
+51.5 difference
GPT-5.2
Mellum2-12B-A2.5B-Instruct
$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-Instruct only becomes the better choice if you would rather avoid the extra latency and token burn of a reasoning model.
GPT-5.2 is clearly ahead on the provisional aggregate, 79 to 27. 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 40.9. The single biggest benchmark swing on the page is GPQA, 92.4% to 40.9%.
GPT-5.2 is the reasoning model in the pair, while Mellum2-12B-A2.5B-Instruct 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. GPT-5.2 gives you the larger context window at 400K, compared with 128K for Mellum2-12B-A2.5B-Instruct.
GPT-5.2 is ahead on BenchLM's provisional leaderboard, 79 to 27. The biggest single separator in this matchup is GPQA, where the scores are 92.4% and 40.9%.
GPT-5.2 has the edge for knowledge tasks in this comparison, averaging 92.4 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
GPT-5.2 has the edge for coding in this comparison, averaging 64.7 versus 37.2. Mellum2-12B-A2.5B-Instruct stays close enough that the answer can still flip depending on your workload.
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