Q. Semantic search keeps missing exact tokens like an error code. What retrieval change fixes it?
A. Hybrid search: run dense (vector) and sparse (BM25 keyword) retrieval together and fuse the scores. BM25 weights the rare exact token while the embedding still handles paraphrase. In Bedrock Knowledge Bases it is a HYBRID search type.
Why? Pure vector search smears rare exact tokens together; hybrid is the direct fix.