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This book teaches you to build a Large Language Model from scratch. Not just use tools like ChatGPT, but understand them, construct them, make them work.

If you're curious about how AI actually works, this book is for you. We assume no prior programming experience and no advanced math. We start from first principles and build up, piece by piece, explaining everything along the way.

The book is organized as one continuous, hands-on project:

Part I: Foundations: What AI and LLMs actually are, how machines process language, and the innovations that made this possible.

Part II: Python Essentials: The programming tools you'll need, nothing more.

Part III: Build Your First LLM: The core of the book. Implement tokenization, embeddings, attention, and the full Transformer architecture from scratch.

Part IV: Make It Useful: Fine-tuning, prompt engineering, and building practical applications.

Part V: Share It With the World: Deploying your creation so others can use it.

Every concept is explained before it's coded. We use analogies to make abstract ideas concrete. Every line of code is justified. We don't skip steps, and we don't hand-wave.

Every chapter includes a companion notebook that runs in Google Colab (no installation, no setup on your computer, just click and start coding).

Each chapter ends with review questions to test your understanding, with all answers provided in Appendix D. Notebooks are also available on GitHub at https://github.com/FirstLLM/code.

Understanding comes through doing. The concepts will make sense because you'll build them yourself.

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