"Why did checkout start failing after Tuesday's deploy?"
RAG, step 1: search once
The whole question goes to search. The top hits are the checkout runbook and an old incident report, because they share the most words with the question.
RAG, step 2: answer
The model answers from those pages. Nothing about Tuesday's change was retrieved, so the answer repeats the old incident. One search, one model call.
Agentic RAG, step 1: plan
The agent splits the question in two: what changed on Tuesday, and what do the checkout errors say?
Agentic RAG, step 2: search the deploy notes
Query: "deploy Tuesday checkout". Hit: "payment client timeout lowered from 30s to 5s".
Agentic RAG, step 3: search the logs
Query: "checkout error timeout". Hit: "PaymentGateway call timed out after 5000 ms", starting Tuesday.
Agentic RAG, step 4: judge and answer
Two sources agree, so it answers and cites both. If neither search had matched, it should rewrite the query once more or say "not found" instead of guessing.
The cost
Here RAG used one search and one model call. The agent used two searches and three model calls: plan, judge and answer. More rounds cost more.