Large Language Models (LLM) & AI Market: JetBrains Releases Mellum2 12B Mixture-of-Experts Model

JetBrains announced Mellum2, an open-source 12-billion-parameter model based on a Mixture-of-Experts (MoE) architecture released June 1, 2026. Mellum2 activates only ~2.5 billion parameters per inference, which the team says yields inference speeds over twice as fast than equivalent-scale models and reduces deployment costs. The model is optimized for text and code (no multimodal inputs), positioned as a "focused" model for multi-model collaboration systems handling tasks like prompt classification, tool selection, context compression for RAG pipelines, sub-agent planning validation, and code completion. Mellum2 is released under the Apache 2.0 license; a technical report is on arXiv (ID 2605.31268) and model weights are available on HuggingFace. Benchmarks reportedly show competitive performance among open-source models of similar scale.