Instella: Fully Open Language Models with Stellar Performance
Authors: name: Jiang Liu; name: Jialian Wu; name: Xiaodong Yu; name: Yusheng Su; name: Prakamya Mishra; name: Gowtham Ramesh; name: Sudhanshu Ranjan; name: Chaitanya Manem; name: Ximeng Sun; name: Ze Wang; name: Pratik Prabhanjan Brahma; name: Zicheng Liu; name: Emad Barsoum
Published: 2025-11-13 18:52:46

Abstract: Large language models (LLMs) have demonstrated remarkable performance across a wide range of tasks, yet the majority of high-performing models remain closed-source or partially open, limiting transparency and reproducibility. In this work, we introduce Instella, a family of fully open three billion parameter language models trained entirely on openly available data and codebase. Powered by AMD Instinct MI300X GPUs, Instella is developed through large-scale pre-training, general-purpose instruction tuning, and alignment with human preferences. Despite using substantially fewer pre-training tokens than many contemporaries, Instella achieves state-of-the-art results among fully open models and is competitive with leading open-weight models of comparable size. We further release two specialized variants: Instella-Long, capable of handling context lengths up to 128K tokens, and Instella-Math, a reasoning-focused model enhanced through supervised fine-tuning and reinforcement learning on mathematical tasks. Together, these contributions establish Instella as a transparent, performant, and versatile alternative for the community, advancing the goal of open and reproducible language modeling research.