OpenAI. Three minutes with the o1 team describing the moment the model started questioning its own reasoning during RL training. Useful as the primary source for the article's claim that the chain-of-thought is now happening inside the model, not in your prompt.
Keep this as historical source material, not as current implementation guidance. It explains why the category emerged, but production choices should be based on the current model lineup and API docs.
See the original product/research framing that made reasoning models different from ordinary chat models.
Watch the primary pick first or read the companion article's reasoning-model section.
Continue through the same learning path with the next curated companion videos.