To RAG or to Fine-Tune? Picking the Right Tool for the AI Job
When you need an LLM to use your knowledge or behave a specific way, two approaches dominate the conversation: RAG (retrieval-augmented generation) and fine-tuning. They sound interchangeable and they’re not — they solve different problems and have very different cost, complexity, and maintenance profiles. Getting RAG vs fine-tuning right early saves you a lot of wasted GPU budget. Here’s the honest comparison. The one-line difference RAG changes what the model knows right now by injecting relevant documents into the prompt at query time. The model’s weights never change. Fine-tuning changes how the model behaves by updating its weights on your examples. Knowledge problem → reach for RAG. Behavior/format/style problem → consider fine-tuning. Most “the AI doesn’t know our stuff” issues are knowledge problems. ...