Sebastian Raschka

Build A Reasoning Model Scratch 1: Motivation & Code Setup

Published 2026-08-30 · Duration 43:27

Summary

This video introduces the concept of reasoning models, detailing their evolution from conventional LLMs and how they are utilized within agent harnesses. The core focus is on the educational value of implementing these complex systems 'from scratch' to gain a deep understanding of underlying mechanisms (e.g., reinforcement learning, distillation). Practical steps include setting up the development environment using `uv` for dependency management and PyTorch/JupyterLab for coding.

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Key takeaways

  1. LLM Evolution 2:00

    The progression moves from conventional LLMs to reasoning models, which are modified versions of regular LLMs. These reasoning models form the 'engine' used by modern agent harnesses (e.g., OpenAIs Code Agent) [1:16].

  2. Value of From Scratch Learning 8:23

    Implementing models from scratch provides unambiguous, precise code examples that are highly valuable for deep learning understanding, serving as a 'proof' beyond mere conceptual images [8:23].

  3. Setup Workflow 20:40

    The recommended setup involves cloning the GitHub repository and using `uv` (a fast dependency manager) to sync dependencies within an isolated virtual environment before running code in JupyterLab or VS Code [20:40].

Technical details

  • Model Architecture 120s

    Reasoning models are essentially modified LLMs, capable of complex reasoning tasks that conventional LLMs lacked. The architecture remains fundamentally an LLM [1:16].

  • Dependency Management 1240s

    The speaker recommends using `uv` over traditional `pip install -r requirements.txt` because it manages virtual environments and dependencies (via a lock file) more efficiently, ensuring project isolation and speed [20:40].

  • Hardware Acceleration 1032s

    When running code, check for CUDA GPU support using `torch.cuda.is_available()`. For Apple Silicon devices, the MPS (Metal Performance Shader) framework is used for acceleration; however, convergence issues were noted when training on MPS compared to CPU/CUDA [19:45].

  • Training Techniques 976s

    Advanced reasoning model development involves techniques like Reinforcement Learning and Distillation (using structured data from another LLM to train a smaller, efficient model) [18:18].

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