System Instructions
Hidden directives loaded into an AI session that shape the model's behavior, tone, and constraints. They consume context window tokens like any other input.
System instructions are the invisible setup text that tells a model how to behave. They persist across every turn but users never see them. Long system prompts eat into the available context window before the conversation even starts, which is why models with complex configurations can feel sluggish earlier than expected.
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Related Terms
Context Window
The total amount of text, code, and conversation history an AI model can hold in active memory during a single session. Measured in tokens, not words.
AI Token
The basic unit of text that AI language models process. Roughly 0.75 words per token in English, though the ratio varies by language and content type.
Prompt
The input text, question, or instruction given to an AI model to generate a response. The quality of the prompt directly shapes the quality of the output.