LLM reasoning models have the power to tackle truly challenging problems that require finding the right path through multiple steps. In this book you’ll learn how to build a working reasoning model from the ground up. You will start with an existing pre-trained LLM and then implement reasoning-focused improvements from scratch.
Sebastian Raschka, the bestselling author of Build a Large Language Model (From Scratch), is your guide on this exciting journey. Sebastian mentors you every step of the way with clear explanations, practical code, and a keen focus on what really matters. Understand LLM reasoning by creating your own reasoning model–from scratch!
In Build A Reasoning Model (From Scratch) you’ll learn how
• Implement core reasoning improvements for LLMs • Evaluate models using judgment-based and benchmark-based methods • Improve reasoning without updating model weights • Use reinforcement learning to integrate external tools like calculators • Apply distillation techniques to learn from larger reasoning models • Understand the full reasoning model development pipeline
Reasoning models break problems into steps, producing more reliable answers in math, logic, and code. These improvements aren’t just a curiosity–they’re already integrated into top models like Grok 4 and GPT-5. Build A Reasoning Model (From Scratch) demystifies these complex models with a simple the best way to learn how something works is to build it yourself! You’ll begin with a pre-trained LLM, adding and improving its reasoning capabilities in ways you can see, test, and understand.
About the book
In Build a Reasoning Model (From Scratch), acclaimed ML research engineer Sebastian Raschka takes you inside the black box of reasoning-enhanced LLMs. You’ll start with a compact, pre-trained base model that runs on consumer hardware, then upgrade it step by step to tackle ever-more difficult problems and scenarios. You’ll measure its performance, add reasoning at inference time without training, and then improve it further with reinforcement learning. By the end of the book, you’ll have a small but capable reasoning stack built from the ground up!
About the reader
For readers who know Python and have some knowledge of machine learning. You won’t need any specialist hardware. The examples will run on a standard laptop, although using cloud GPUs can make training faster.
About the author
Sebastian Raschka, PhD, is an LLM Research Engineer with over a decade of experience in artificial intelligence. His work spans industry and academia, including implementing LLM solutions as a senior engineer at Lightning AI and teaching as a statistics professor at the University of Wisconsin–Madison.
Sebastian collaborates with industry partners on AI solutions and serves on the Open Source Board at University of Wisconsin–Madison. He specializes in LLMs and the development of high-performance AI systems, with a deep focus on practical, code-driven implementations. He is the author of the bestselling books Build a Large Language Model (From Scratch), as well as Machine Learning with PyTorch and Scikit-Learn, and Machine Learning Q and AI.
Some of my greatest passions are "Data Science" and machine learning. I enjoy everything that involves working with data: The discovery of interesting patterns and coming up with insightful conclusions using techniques from the fields of data mining and machine learning for predictive modeling.
I am a big advocate of working in teams and the concept of "open source." In my opinion, it is a positive feedback loop: Sharing ideas and tools that are useful to others and getting constructive feedback that helps us learn!
A little bit more about myself: Currently, I am sharpening my analytical skills as a PhD candidate at Michigan State University where I am currently working on a highly efficient virtual screening software for computer-aided drug-discovery and a novel approach to protein ligand docking (among other projects). Basically, it is about the screening of a database of millions of 3-dimensional structures of chemical compounds in order to identifiy the ones that could potentially bind to specific protein receptors in order to trigger a biological response.
In my free-time I am also really fond of sports: Either playing soccer or tennis in the open air or building models for predictions. I always enjoy creative discussions, and I am happy to connect with people. Please feel free to contact me by email or in one of those many other networks!
Sebastian's books are really the ones you should read if you learn by building...I am guessing they will be two in a small set of AI / LLM books that will stay current (at least longer than others) as they focus on the basics and building at a lower level which will require a algo innovation to be replaced by something newer than like others sharing the (hype) patterns of the day e.g. X10 prompt engineering books...