The one-sentence takeaway

DeepSeek-R1 showed that a model can teach itself to reason, growing longer chains of thought and self-checking habits on its own, when it is trained with reinforcement learning and rewarded simply for reaching verifiably correct answers, with a light touch of clean example data added only to tidy up how it presents its thinking.

Next: Chapter 5, Recursive Language Models, where a model learns to handle inputs far larger than its own memory.