What is hybrid retrieval and do I need it?

Hybrid retrieval combines vector search (semantic meaning) with BM25 keyword search (lexical match). Atlas supports both natively (Atlas Search for BM25, Atlas Vector Search for vectors). Hybrid retrieval typically beats vector-only by 10 to 20% on retrieval quality for RAG applications because it catches both meaning matches and exact keyword matches (product SKUs, error codes, proper nouns, product names). Ranking is done via reciprocal rank fusion. For serious RAG apps or product search with SKU-like terms, hybrid is worth the extra engineering effort. For basic semantic search over natural-language documents, vector-only is often enough.