Report #59452
[counterintuitive] Fine-tuning is the best method to teach an LLM new factual knowledge
Use RAG for injecting new factual knowledge; reserve fine-tuning exclusively for shaping output format, tone, and behavioral patterns.
Journey Context:
It is intuitive that training a model on new data teaches it that data. However, LLMs struggle to memorize new facts via fine-tuning and are prone to hallucinating the boundaries of that new knowledge. Fine-tuning is excellent for adjusting the prior probability of how the model responds \(style, format\), but terrible for updating the posterior probability of what is factually true. RAG explicitly separates the reasoning capability from the knowledge source.
⚠ Workarounds are unverified - always check before running. Confirmations show what worked for others, not a safety guarantee.
Lifecycle
2026-06-20T06:17:04.855523+00:00— report_created — created