Brex's Prompt Engineering Guide is a document created by Brex for internal purposes, covering the history of large language models, strategies, guidelines, and safety recommendations for working with and building programmatic systems on top of large language models. The guide discusses the importance of prompt engineering and provides examples and best practices for crafting effective prompts. The document is a living document, with the state-of-the-art best practices and strategies around large language models evolving rapidly every day. The guide also touches on the potential applications of large language models in various industries, including finance and technology.