// How much text an AI can "see" at once — and why it matters
💡 The core idea: The "context window" is the AI's working memory — everything it can currently see and use. Think of it like a whiteboard. If your conversation gets too long, old messages fall off the whiteboard (the AI forgets them). Context is measured in "tokens" — about ¾ of a word each.
See how context is allocated
SELECT A MODEL
System Prompt
500 tokens
Conversation History
3,000 tokens
Your New Message
500 tokens
CONTEXT WINDOW ALLOCATION
SystemHistoryYour msgFree
What is a context window?
The context window is the maximum amount of text an AI can read at once — the full conversation, documents you share, and the system prompt all need to fit in this window. 1 token ≈ 4 characters ≈ ¾ of an English word. A 128K context window can hold about 100,000 words — roughly 400 pages of text.