Reranking Models and Late-Interaction Frameworks in Production RAG: Comparing Cohere Rerank 3.5, BGE-Reranker-v2, FlashRank, and ColBERTv2 Architecture, Cross-Encoder Latency, MaxSim Compression, and Retrieval Economics
In production Retrieval-Augmented Generation (RAG), relying solely on first-stage bi-encoder dense embeddings or lexical BM25 search creates a structural information bottleneck. First-stage retrieval compresses an entire document passage into a single fixed-dimensional vector (such as 768, 1024, or 1536 dimensions) or an inverted term index. This independent encoding decouples the query from the passage during indexing, eliminating token-level cross-attention and causing subtle semantic nuances,









