Head-to-head comparison across 1benchmark categories. Overall scores shown here use BenchLM's provisional ranking lane.
GPT-5.3 Codex
86
Mellum2-12B-A2.5B-Thinking
59
Pick GPT-5.3 Codex if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority.
Coding
+6.8 difference
GPT-5.3 Codex
Mellum2-12B-A2.5B-Thinking
$1.75 / $14
N/A
79 t/s
N/A
88.26s
N/A
400K
128K
Pick GPT-5.3 Codex if you want the stronger benchmark profile. Mellum2-12B-A2.5B-Thinking only becomes the better choice if coding is the priority.
GPT-5.3 Codex is clearly ahead on the provisional aggregate, 86 to 59. The gap is large enough that you do not need to squint at the spreadsheet to see the difference.
GPT-5.3 Codex gives you the larger context window at 400K, compared with 128K for Mellum2-12B-A2.5B-Thinking.
GPT-5.3 Codex is ahead on BenchLM's provisional leaderboard, 86 to 59.
Mellum2-12B-A2.5B-Thinking has the edge for coding in this comparison, averaging 69.9 versus 63.1. GPT-5.3 Codex 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.