Head-to-head comparison across 3benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Opus 4.5
76
Mellum2-12B-A2.5B-Instruct
27
Verified leaderboard positions: Claude Opus 4.5 #14 · Mellum2-12B-A2.5B-Instruct unranked
Pick Claude Opus 4.5 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Instruct only becomes the better choice if its workflow or ecosystem matters more than the raw scoreboard.
Coding
+28.7 difference
Knowledge
+25.3 difference
Inst. Following
+3.6 difference
Claude Opus 4.5
Mellum2-12B-A2.5B-Instruct
$5 / $25
N/A
46 t/s
N/A
1.01s
N/A
200K
128K
Pick Claude Opus 4.5 if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Instruct only becomes the better choice if its workflow or ecosystem matters more than the raw scoreboard.
Claude Opus 4.5 is clearly ahead on the provisional aggregate, 76 to 27. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Claude Opus 4.5's sharpest advantage is in coding, where it averages 65.9 against 37.2. The single biggest benchmark swing on the page is GPQA, 87% to 40.9%.
Claude Opus 4.5 gives you the larger context window at 200K, compared with 128K for Mellum2-12B-A2.5B-Instruct.
Claude Opus 4.5 is ahead on BenchLM's provisional leaderboard, 76 to 27. The biggest single separator in this matchup is GPQA, where the scores are 87% and 40.9%.
Claude Opus 4.5 has the edge for knowledge tasks in this comparison, averaging 66.2 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
Claude Opus 4.5 has the edge for coding in this comparison, averaging 65.9 versus 37.2. Mellum2-12B-A2.5B-Instruct stays close enough that the answer can still flip depending on your workload.
Claude Opus 4.5 has the edge for instruction following in this comparison, averaging 79.4 versus 75.8. Inside this category, IFEval is the benchmark that creates the most daylight between them.
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