JetBrains Releases Mellum2: 12B Parameter Mixture-of-Experts Architecture Developer-Focused Model
AI News Flash: JetBrains released Mellum2 on June 1, 2026—a 12-billion parameter open-source model based on Mixture-of-Experts (MoE) architecture, but it only activates 2.5 billion active parameters per inference, making inference over twice as fast as models of equivalent scale, significantly reducing deployment costs, released under Apache 2.0 license. Mellum2 isn’t positioned as a replacement for frontier large models, but rather as a ‘focused model’ in multi-model collaboration systems, handling high-frequency lightweight tasks including prompt classification, tool selection, context compression and summarization for RAG pipelines, sub-agent planning validation, and code completion. The model processes only text and code modalities, deliberately excluding multimodal capabilities to keep the architecture lean—particularly suitable for enterprises deploying in private environments to handle internal code and confidential data. Across multiple benchmarks including code generation, reasoning, science, and math, Mellum2 achieves competitive performance among open-source models of similar scale. The technical report has also been published on arXiv (编号 2605.31268), and model weights are available for download on HuggingFace.