
Both ground a model in your knowledge — but they solve different problems. Here is how to decide.
RAG retrieves your content at query time and feeds it to the model as context. Fine-tuning updates the model's weights on your data. If you need answers grounded in changing, permission-scoped documents, choose RAG. If you need a consistent style, format, or domain behavior, fine-tune.
RAG wins for knowledge-heavy use cases: support, compliance, internal search. Documents can be updated without retraining, and retrieval can respect who is asking.
Fine-tuning wins when you need reliable output format, tone, or domain-specific behavior — and your data is stable. It also reduces token cost by making the model more concise.
Many production systems do both: fine-tune for behavior, RAG for knowledge. Start with RAG alone — it is faster to ship and easier to evaluate.
RAG is usually cheaper to start — no training compute, and retrieval costs are modest. Fine-tuning adds training cost but can lower per-token inference cost over time.
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