Running Mellum2.1 Locally for CI Repair: Where a 12B MoE Model Holds Up

JetBrains' Mellum2.1, a 12B MoE open-weight coding agent model reporting 47% on SWE-Bench, is worth running locally for narrow CI repair and PR-review loops — but only if you understand where its sparse-activation architecture and small active-parameter budget stop being enough.