Head-to-head comparison across 1benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
GPT-5.5 Pro
100
Mellum2-12B-A2.5B-Thinking
59
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if knowledge is the priority.
Knowledge
+0.4 difference
GPT-5.5 Pro
Mellum2-12B-A2.5B-Thinking
$30 / $180
N/A
N/A
N/A
N/A
N/A
1M
128K
Pick GPT-5.5 Pro if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if knowledge is the priority.
GPT-5.5 Pro is clearly ahead on the provisional aggregate, 100 to 59. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.5 Pro gives you the larger context window at 1M, compared with 128K for Mellum2-12B-A2.5B-Thinking.
GPT-5.5 Pro is ahead on BenchLM's provisional leaderboard, 100 to 59.
Mellum2-12B-A2.5B-Thinking has the edge for knowledge tasks in this comparison, averaging 57.6 versus 57.2. GPT-5.5 Pro stays close enough that the answer can still flip depending on your workload.
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