This report examines what I see as the core argument for concern about existential risk from misaligned artificial intelligence. I proceed in two stages. First, I lay out a backdrop picture that informs such concern. On this picture, intelligent agency is an extremely powerful force, and creating agents much more intelligent than us is playing with fire – especially given that if their objectives are problematic, such agents would plausibly have instrumental incentives to seek power over humans. Second, I formulate and evaluate a more specific six-premise argument that creating agents of this kind will lead to existential catastrophe by 2070. On this argument, by 2070: (1)  it will become possible and financially feasible to build relevantly powerful and agentic AI systems; (2)  there will be strong incentives to do so; (3)  it will be much harder to build aligned (and relevantly powerful/agentic)  AI systems than to build misaligned (and relevantly powerful/agentic)  AI systems that are still superficially attractive to deploy; (4)  some such misaligned systems will seek power over humans in high-impact ways; (5)  this problem will scale to the full disempowerment of humanity; and (6)  such disempowerment will constitute an existential catastrophe. I assign rough subjective credences to the premises in this argument, and I end up with an overall estimate of ~5% that an existential catastrophe of this kind will occur by 2070.(May 2022 update: since making this report public in April 2021, my estimate here has gone up, and is now at >10%.) 