Mellum2.1
JetBrains released Mellum2.1, an open 12B mixture-of-experts model for coding agents. Its post-training uses reinforcement learning in real coding environments, enabling it to explore repositories, edit files, and check its changes; the model is available on Hugging Face under Apache 2.0.
For buildersTry it on a representative codebase task that includes diagnosing a failing test, proposing a patch, and checking the result; compare quality and latency with your current coding model.