Context Window Explained — What LLMs Can "Remember"
The context window is the total amount of text an LLM can see at once — both your input and its output. Understanding it helps you avoid "forgetting" issues and use AI tools more effectively.
TL;DR: The context window is the total amount of text an LLM can see at once — both your input and its output. Understanding it helps you avoid "forgetting" issues and use AI tools more effectively.
What Is the Context Window?
Think of the context window as the AI's working memory. Everything the model can "see" during a conversation — your messages, its replies, system instructions — must fit within this window, measured in tokens. Once exceeded, the model loses access to earlier content.
Context Windows by Model (2026)
GPT-4o: 128,000 tokens (~96,000 words). Claude 3.5 Sonnet: 200,000 tokens (~150,000 words). Gemini 1.5 Pro: 1,000,000 tokens (~750,000 words). Gemini 1.5 Flash: 1,000,000 tokens. GPT-4o-mini: 128,000 tokens.
The "Lost in the Middle" Problem
Research shows LLMs perform best on content at the very beginning and very end of the context window, and worst on content buried in the middle. This "lost in the middle" effect means very long contexts don't always perform proportionally better.
Practical Context Window Strategy
Put your most important instructions at the beginning AND end of your prompt. Use RAG for large document sets instead of stuffing everything into context. Start fresh conversations for completely new topics rather than extending old ones.