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How to Train LLMs to “Think” (o1 & DeepSeek-R1)

Advanced reasoning models explained

Shaw Talebi
9 min readFeb 12, 2025

In September 2024, OpenAI released its o1 model, trained on large-scale reinforcement learning, giving it “advanced reasoning” capabilities. Unfortunately, the details of how they pulled this off were never shared publicly. Today, however, DeepSeek (an AI research lab) has replicated this reasoning behavior and published the full technical details of their approach. In this article, I will discuss the key ideas behind this innovation and describe how they work under the hood.

A thinking laptop.

OpenAI’s o1 model marked a new paradigm for training large language models (LLMs). It introduced so-called “thinking” tokens, which enable a sort of scratch pad that the model can use to think through problems and user queries.

The major insight from o1 was performance improved with increased test-time compute. This is just a fancy way of saying that the more tokens a model generates, the better its response. The figure below, reproduced from OpenAI’s blog, captures this point nicely.

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Shaw Talebi
Shaw Talebi

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