What is multi-hop retrieval in RAG?

Multi-hop retrieval handles questions whose answer requires combining information from multiple documents that are not individually sufficient. The system retrieves an initial set of documents, uses them to refine the query or extract intermediate facts, then retrieves again based on the refined understanding. For example, answering "who founded the company that makes Claude" requires first retrieving that Anthropic makes Claude, then retrieving that Dario and Daniela Amodei founded Anthropic. Multi-hop patterns are central to agentic RAG and research-oriented applications.