GPT-4 vs. GPT-3.5: What's the Difference?

An open letter signed by Elon Musk, Steve Wozniak and a number of top AI scientists is calling for a six-month pause on AI development. Arguing that powerful AI systems should be developed only once we are confident that their effects will be positive and the risks will be manageable. So what is the real difference between GPT-4 and its predecessor? And why does it scare AI experts so much? I'm Sophie Bushwick; you're Kelsel Harper.