Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Opus 4.6
87
Mellum2-12B-A2.5B-Thinking
59
Verified leaderboard positions: Claude Opus 4.6 #7 · Mellum2-12B-A2.5B-Thinking unranked
Pick Claude Opus 4.6 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority or you want the stronger reasoning-first profile.
Coding
+5.5 difference
Knowledge
+18.6 difference
Claude Opus 4.6
Mellum2-12B-A2.5B-Thinking
$5 / $25
N/A
40 t/s
N/A
1.78s
N/A
1M
128K
Pick Claude Opus 4.6 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority or you want the stronger reasoning-first profile.
Claude Opus 4.6 is clearly ahead on the provisional aggregate, 87 to 59. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Claude Opus 4.6's sharpest advantage is in knowledge, where it averages 76.2 against 57.6. The single biggest benchmark swing on the page is GPQA, 91.3% 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.
Mellum2-12B-A2.5B-Thinking is the reasoning model in the pair, while Claude Opus 4.6 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. Claude Opus 4.6 gives you the larger context window at 1M, compared with 128K for Mellum2-12B-A2.5B-Thinking.
Claude Opus 4.6 is ahead on BenchLM's provisional leaderboard, 87 to 59. The biggest single separator in this matchup is GPQA, where the scores are 91.3% and 57.6%.
Claude Opus 4.6 has the edge for knowledge tasks in this comparison, averaging 76.2 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 64.4. Claude Opus 4.6 stays close enough that the answer can still flip depending on your workload.
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