There is a nuanced but important difference between chain-of-thought before and after o1. Before the o1 paradigm (i.e., chain-of-thought prompting), there was a mismatch between what chain of thought was and what we wanted it to be. We wanted chain of thought to reflect the thinking process of the model, but what the model was really doing was just imitating reasoning paths that it had seen in pretraining, e.g., math homework solutions. The problem with this type of data is that it is a post-hoc solution summarized after the author did all the work somewhere else, and not really a sequence of thoughts. So the solutions often had poor information density, with an egregious example being things like “The answer is 5 because…”, where the token “5” has a huge amount of new information. With the o1 paradigm, you can see that the chain of thought looks very different from a textbook math solution (you can view examples in the blog post). These chains of thought are kinda like “inner monologue” or “stream of consciousness”. You can see the model backtracking; it says things like “alternatively, let’s try” or “wait, but”. And I have not measured directly, but I would wager a bet (my psycholinguistics friends would probably be able to confirm) that the information density is *much* more uniform in the chain of thought than average text on the internet.