What's really open about open-weight AI?

Everyone in AI is talking about open-weight models right now. Some see them as the ticket to faster, more efficient development; others see them as an economic threat; they're either a security risk or the only security solution, depending who you ask. The Verge's Robert Hart explains how open-weight models work, why they're suddenly at the center of discussions about AI safety, and whether the only way to stop a bad guy with AI is a good guy with AI.