Haystack is an open-source, modular framework for building production-ready applications that combine large language models, embeddings, and vector search. It provides composable building blocks — models, vector stores, file converters, retrievers, generators and agents — that can be connected into pipelines or multi-agent systems for retrieval-augmented generation (RAG), question answering, semantic search and conversational agents. Haystack emphasizes extensibility and real-world deployment with integrations for many model providers and vector DBs, a curated integrations ecosystem, experimental extensions, and commercial options (deepset Studio and Haystack Enterprise) for visual pipeline development, support and scaling.