JetBrains Open-Sources Mellum2-12B-A2.5B-Thinking, a Sparse Coding Model Tuned for IDE Tooling

Mervin Praison·low signal

As part of June's dense open-weight release window, JetBrains shipped Mellum2-12B-A2.5B-Thinking under Apache 2.0 — a 12B MoE that activates only 8 of 64 experts (~2.5B active), targeting coding quality at much lower active inference width. The 'thinking' variant adds reasoning traces while keeping the active footprint small enough for local IDE integration. For builders wanting an embeddable, latency-sensitive code model, this is a notably efficient open option from a tooling vendor that ships its own IDE.