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Live drop
Mellum2.1
JetBrainsDropped Oct 8, 2026
12B MoE coding model post-trained with RL in real repositories for agentic edit-and-verify loops.
About this release
Live drop
JetBrainsDropped Oct 8, 2026
12B MoE coding model post-trained with RL in real repositories for agentic edit-and-verify loops.
About this release
Mellum2.1 is an Apache 2.0 open-weight 12B mixture-of-experts model (2.5B active parameters) from JetBrains. The update focuses on reinforcement learning in sandboxed code environments, lifting SWE-bench Verified from 2% to 47% while keeping the same architecture and speed as Mellum2. It ships with Thinking, Instruct, and Base checkpoints on Hugging Face and supports vLLM serving with 131K context.
Read the official JetBrains launch pageFirst builds incoming — this lane fills in automatically as people start building with Mellum2.1. Know one? Submit the URL.