Head-to-head comparison across 2benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
GPT-5.4
89
Mellum2-12B-A2.5B-Instruct
27
Verified leaderboard positions: GPT-5.4 #17 · Mellum2-12B-A2.5B-Instruct unranked
Pick GPT-5.4 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
+20.5 difference
Knowledge
+25.2 difference
GPT-5.4
Mellum2-12B-A2.5B-Instruct
$2.5 / $15
N/A
74 t/s
N/A
151.79s
N/A
1.05M
128K
Pick GPT-5.4 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-5.4 is clearly ahead on the provisional aggregate, 89 to 27. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.4's sharpest advantage is in knowledge, where it averages 66.1 against 40.9. The single biggest benchmark swing on the page is GPQA, 92.8% to 40.9%.
GPT-5.4 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-5.4 gives you the larger context window at 1.05M, compared with 128K for Mellum2-12B-A2.5B-Instruct.
GPT-5.4 is ahead on BenchLM's provisional leaderboard, 89 to 27. The biggest single separator in this matchup is GPQA, where the scores are 92.8% and 40.9%.
GPT-5.4 has the edge for knowledge tasks in this comparison, averaging 66.1 versus 40.9. Inside this category, GPQA is the benchmark that creates the most daylight between them.
GPT-5.4 has the edge for coding in this comparison, averaging 57.7 versus 37.2. Mellum2-12B-A2.5B-Instruct stays close enough that the answer can still flip depending on your workload.
For engineers, researchers, and the plain curious — a weekly brief on new models, ranking shifts, and pricing changes.
Free. No spam. Unsubscribe anytime.