In this work, we develop and release Llama 2, a collection of pretrained and fine-tuned large language models (LLMs)  ranging in scale from 7 billion to 70 billion parameters. Our fine-tuned LLMs, calledLlama 2-Chat, are optimized for dialogue use cases. Our models outperform open-source chat models on most benchmarks we tested, and based on our human evaluations for helpfulness and safety, may be a suitable substitute for closed-source models. We provide a detailed description of our approach to fine-tuning and safety improvements ofLlama 2-Chatin order to enable the community to build on our work and contribute to the responsible development of LLMs.