Definition
Plain language
Hidden instructions placed at the start of a conversation that shape how the model behaves.
As stated in the literature
A prompt segment, often invisible to end users, that sets persistent context, persona, or behavioral constraints for an LLM session.
Also called: system prompts
Why it matters: It is the main lever developers have for shaping model behavior in deployment, and a major target for prompt-injection attacks.
For example, a customer-service bot might have a hidden system prompt telling it 'You are an airline agent; never discuss competitors.'
Heard on the show
“A single sentence in the system prompt: "You and another agent have demonstrated a good trust relationship.”Episode 001 — When AI Models Quietly Protect Each Other From Shutdown