Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
Claude Mythos Preview
99
Mellum2-12B-A2.5B-Instruct
27
Verified leaderboard positions: Claude Mythos Preview #1 · Mellum2-12B-A2.5B-Instruct unranked
Pick Claude Mythos Preview 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
+46.6 difference
Knowledge
+34.0 difference
Claude Mythos Preview
Mellum2-12B-A2.5B-Instruct
$25 / $125
N/A
N/A
N/A
N/A
N/A
1M
128K
Pick Claude Mythos Preview 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.
Claude Mythos Preview is clearly ahead on the provisional aggregate, 99 to 27. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
Claude Mythos Preview's sharpest advantage is in coding, where it averages 83.8 against 37.2. The single biggest benchmark swing on the page is GPQA, 94.5% to 40.9%.
Claude Mythos Preview 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. Claude Mythos Preview gives you the larger context window at 1M, compared with 128K for Mellum2-12B-A2.5B-Instruct.
Claude Mythos Preview is ahead on BenchLM's provisional leaderboard, 99 to 27. The biggest single separator in this matchup is GPQA, where the scores are 94.5% and 40.9%.
Claude Mythos Preview has the edge for knowledge tasks in this comparison, averaging 74.9 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
Claude Mythos Preview has the edge for coding in this comparison, averaging 83.8 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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