Dario Amodei, the chief executive of the artificial intelligence company Anthropic, published a 3,800-word open letter on Saturday calling for a slowdown in the development of A.I. The essay prompted other A.I. leaders, including Sam Altman, the chief executive of OpenAI; Elon Musk, SpaceX’s chief executive; and Demis Hassabis, the chair of Google DeepMind, to speak out in agreement. Here are the key arguments that Mr. Amodei made in his essay: Why A.I. Needs to Slow Down Mr. Amodei said two recent developments convinced him that simply investing in A.I.…