On July 25, Jeff Dean spoke to 6,000 would-be founders at Y Combinator’s Startup School at San Francisco’s Chase Center. Dean is a legendary engineer at Google. He is cofounder of Google Brain, chief scientist of Google DeepMind and Google Research, and technical colead on the company’s flagship AI model Gemini. With his frequent collaborator Sanjay Ghemawat, he’s written significant parts of the company’s computing and search infrastructure. A running joke in geekdom is a list of surreal “facts...