JetBrains Releases Mellum2.1, a 12B MoE Open Model Built for Coding Agents

JetBrains has released Mellum2.1, a 12-billion-parameter Mixture-of-Experts open model specifically architected for coding agent use cases. The model is designed to handle multi-step code generation, refactoring, and tool-use patterns that modern agentic coding workflows demand, with MoE efficiency allowing more capable reasoning at lower inference cost. As an open release, Mellum2.1 is directly available for developers to self-host, fine-tune, or integrate into custom coding pipelines without API dependency. This positions JetBrains as a serious contributor to the open coding model ecosystem alongside offerings from Mistral, DeepSeek, and others. Teams building internal developer tools or coding agents should evaluate Mellum2.1 as a strong open alternative to proprietary coding models.