← Concept IndexDEFINITION WHY IT MATTERS COMMONLY CONFUSED WITH
System prompts vs. training
Also called: custom instructions, system message
A system prompt is standing instruction text placed at the top of the context to steer behaviour for a session or product. It shapes output without changing any weights.
It's the fastest, cheapest way to adapt a model — and the first thing to reach for before fine-tuning. But because it lives in the context, it can also be overridden by cleverly crafted input (prompt injection).
Fine-tuning. A system prompt is temporary context; fine-tuning permanently alters the model.