Llama 2 is a state-of-the-art open-source large language model that can be used for chatbots, and it comes pre-tuned for chat applications in three different sizes: 7B, 13B, and 70B. LangChain is a toolkit that allows developers to build with LLMs like Llama 2, using closed-source models or open-source models like Llama 2. The tutorial adapts the Create a ChatGPT Clone notebook from the LangChain docs, but instead of asking the model to behave as a Linux terminal, it asks Llama 2 to behave as an NPC for a video game. Llama 2 has a context window of 4,096 tokens, which is twice as much as Falcon and equal to the base version of GPT-3.5. LangChain lets developers take advantage of Llama 2's large context window to build a chatbot with just a few lines of code. The tutorial goes through building a chatbot that takes advantage of Llama 2's large context window, using Baseten to host Llama 2 for inference and the latest versions of the necessary Python packages.