map reduce

Two forces decide this design: documents longer than the context window, and summaries that must not lie. The strong answer pairs hierarchical map-reduce with claim-level grounding, then serves it cheaply at scale.

Summarizing a 200-page contract is not one LLM call: it is chunking, hierarchical reduction, and a faithfulness check so you never invent facts. Learn the map-reduce pattern, when long-context beats it, and how to evaluate summaries at scale.