The article discusses the development of reasoning models, a specialization of large language models (LLMs) that enables them to excel at complex tasks such as solving puzzles, advanced math, and coding challenges. It outlines four main approaches to building and improving reasoning models, including inference-time scaling, pure reinforcement learning, supervised fine-tuning and reinforcement learning, and pure supervised fine-tuning and distillation. The article also provides an overview of the DeepSeek R1 pipeline, a case study for developing reasoning LLMs. The development of reasoning models is a rapidly evolving field, with various approaches being explored to enhance the reasoning capabilities of LLMs.