What is reranking in a RAG pipeline, and why does a cross-encoder reranker improve results?

Reranking is the cheapest large win in RAG quality: retrieve broadly, then reorder precisely. The signal is the bi-encoder-versus-cross-encoder distinction and the retrieve-then-rerank two-stage design. Here is the answer.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.