ModelRefs / System Prompt — AI Glossary
System Prompt — AI Glossary
A high-priority instruction message that frames the model's role, constraints, and behavior for the entire conversation.
Overview
System prompts are weighted more heavily than user messages by modern chat models. They are the primary lever for persona, refusal policy, output format, and tool selection. Many providers cache system prompts (prompt caching) to cut per-request cost.
Reference details
| Topic | prompting |
|---|---|
| Last reviewed | 2026-06-24 |
Related terms
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Frequently asked questions
What is System Prompt?
A high-priority instruction message that frames the model's role, constraints, and behavior for the entire conversation.
What concepts are related to System Prompt?
Closely related concepts include prompt engineering, prompt caching.