What Is a Context Window? (And Why Long Prompts Break) — [AI Stack 04]

A context window is the maximum amount of text, measured in tokens, that an AI model can hold in mind at once — its prompt, the conversation so far, and the answer it is writing all have to fit inside it. Episode 4 of The AI Stack explains what a context window is, why it is limited, what really happens when you overflow it, and the "lost in the middle" effect where models stop reliably using the middle of a long prompt. We cover the real 2026 numbers — from 200K tokens up to Gemini's 2 million and Llama 4 Scout's 10 million — and how models are being extended. ▶ The AI Stack — full course in order: [playlist] ← Previous: [AI Stack 03] How Vector Embeddings Turn Words Into Meaning → Next: [AI Stack 05] Temperature & Top-p: The Controls Behind AI "Creativity" #contextwindow #LLM #AItokens