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Llama 2 is a family of large language models (LLMs) from Meta AI, available for free for research and commercial use. It includes pretrained and fine-tuned models with sizes ranging from 7 billion to 70 billion parameters, offering a versatile toolkit for developers.

Its open and permissive license is the key differentiator. Unlike API-only models, Llama 2 can be downloaded and run locally, providing greater control, customization, and privacy. The license allows free commercial use, enabling companies to build proprietary applications without high API costs.

Llama 2 was trained on a massive dataset of 2 trillion tokens from publicly available online sources. Its fine-tuned chat models, Llama 2-Chat, also used Reinforcement Learning with Human Feedback (RLHF), where human annotators rated responses for helpfulness and safety to guide the model's outputs.

The largest model, Llama 2 70B, performs on par with or better than some closed-source models like GPT-3.5 on various benchmarks, excelling at summarization and translation. However, its limitations include the potential for factual inaccuracies (hallucinations) and inheriting biases from its training data.

It serves as a catalyst for innovation by lowering the barrier for building AI applications, fostering a more competitive ecosystem. It allows researchers to study a top-tier LLM's inner workings and gives businesses a cost-effective, private alternative to API-based services, accelerating global AI development.