The Haystack framework, developed by Berlin-based startup Deepset, is an open source tool that allows developers to build advanced AI applications using large language models (LLMs). Founded in 2018 by Milos Rusic and Malte Pietsch, Deepset gained early attention for its focus on natural language processing (NLP) solutions, such as training the first German BERT model. Haystack has since evolved into a powerful tool for building custom applications like question answering, semantic search, and Retrieval-Augmented Generation (RAG) systems.