Cross-Encoder vs Bi-Encoder Reranking (ANSWERED)
Medium RAG interview question on cross-encoder vs bi-encoder reranking — architecture, trade-offs, eval, and production patterns.
TL;DR — Quick Answer
Bi-encoders embed queries and documents independently for fast ANN search at scale. Cross-encoders jointly encode query–passage pairs for sharper relevance scoring but at O(n) cost. Production stacks retrieve with bi-encoders then rerank only the top 20–50 candidates with a cross-encoder before LLM generation.
The Interview Question
Explain cross-encoder vs bi-encoder reranking. How would you design, implement, and evaluate this in a production RAG system? Discuss trade-offs and failure modes.
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