RAG, and the case where you should not use it
Retrieval augmented generation is the right tool for text that does not change, and the wrong tool for anything with a current value, because a retrieval step answers from a copy made at indexing time rather than from the source.
RAG puts your documents into a store, finds the relevant pieces at question time, and hands them to a model. For documents it is the right shape, and it is applied to a great many things that are not documents.
What retrieval actually is
It is a search over a snapshot. You take content, split it, embed it, store it, and later find the nearest pieces to a question. Every part of that assumes the content was worth freezing, which is true of a contract, a manual or a policy, and false of a price, a balance or a status.
The failure is silent and it is the same failure every time
The model answers confidently from the version it was given. Nothing errors. Nothing looks stale, because the retrieved text is well formed and relevant and simply out of date. The system has no way to know, because there is no step in it whose job is to notice that the world moved.
If it has a current value, call it
A function that fetches the number at question time is simpler than a retrieval pipeline, has no indexing job to fall behind, and fails loudly when the source is down instead of quietly serving yesterday. Model providers all support tool calls now. For anything with a live value, that is the shape.
The mixed case, which is most real systems
Retrieve the parts that do not change, call for the parts that do. The policy document goes in the store. The current rate does not. Splitting on that line rather than putting everything through one mechanism is what stops a system that was accurate in testing from drifting quietly in production.
The question that decides it
Ask what happens if this answer is a week old. If the answer is nothing much, retrieval is fine. If the answer is that someone acts on a wrong number, no amount of chunking or reranking fixes it, because the problem is not retrieval quality. The figures below this page are read at request time for exactly that reason.
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