Apropos of nothing, I'm reminded of the "<antthinking>" tags originally observed in Sonnet 3.5's system prompt, and this section of Dario's recent essay (bolding mine):

In 2024, the idea of using reinforcement learning (RL) to train models to generate chains of thought has become a new focus of scaling. Anthropic, DeepSeek, and many other companies (perhaps most notably OpenAI who released their o1-preview model in September) have found that this training greatly increases performance on certain select, objectively measurable tasks like math, coding competitions, and on reasoning that resembles these tasks.