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Chapter 2 · LLM Fundamentals

AI Tokens Explained: Free Beginner Lessons

The tiny pieces models read, and why length and cost depend on them.

  1. Lesson 1

    What Is a Token in AI? Tokens Explained Simply

    Tokens are the small chunks of text AI models read and write. Learn what a token is and the rule of thumb: one token is about four characters.

  2. Lesson 2

    How Many Tokens Is a Word? Counting AI Tokens

    Estimate token counts fast: about 0.75 words per token in English. Learn why names, code, and other languages use more tokens.

  3. Lesson 3

    Context Window Explained: Why AI Forgets

    What is a context window in AI? Learn what counts toward the limit, why long chats make models forget, and what bigger windows really change.

  4. Lesson 4

    AI Token Pricing: Input vs. Output Tokens

    How AI APIs charge per token, why output tokens usually cost more, and simple ways to cut costs without losing useful context.

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