Prompt vs RAG vs fine-tune

Prompting changes instructions, RAG changes knowledge at query time, fine-tuning changes behaviour. Try them in that order.

Stable: this rarely changes. Reviewed 17 Oct 2026.

Key ideas

• RAG for facts that change or must be cited.
• Fine-tuning for consistent format, tone, domain style, or to make a small model match a large one on a narrow task.
• Fine-tuning is poor at adding new factual knowledge reliably.
• Prerequisites: a solid eval set, several hundred to thousands of quality examples, and a plan to retrain when base models change.

Common mistakes

• Fine-tuning before exhausting prompt and retrieval improvements.