Existential risks threaten all of humanity’s future. They are often anthropogenic and tied to future technologies. Even small reductions in such risk have enormous expected value. Natural risks like asteroids are now very unlikely in the near term. Anthropogenic risks from biotech, nanotech and machine intelligence may dominate. Uncertainty in risk assessment itself can amplify perceived risk. Existential risks have pan-generational scope and crushing severity. Their worst harm is destroying humanity’s long-term potential. Earth could sustain at least 10^16 human lives. Future potential could be vastly larger with space or digital minds. The maxipok rule prioritises reducing existential risk above all else. Sustainability should aim for a sustainable trajectory, not a static state. Some risks can be mitigated today but capacity building is more important.

• 10–20% existential risk this century
• 10^16 potential human lives on Earth
• 10^34 to 10^54+ potential future life-years