Reasoning
As of mid-2026, AI-generated content is growing rapidly but meaningful detection and platform policies remain in place. Major platforms (Meta, X, TikTok, YouTube) have invested in detection systems and require disclosure of synthetic media in many jurisdictions. However, the 18-month timeframe to end-2028 is relatively short for crossing the 50% threshold on *new* posts across major platforms simultaneously. Current trajectory suggests AI-generated content comprises roughly 5-15% of posts on major platforms (2026 estimates), requiring 3-10x growth in relative volume. This is technically possible given exponential AI improvement and reduced friction costs, but would require either major policy reversals or widespread evasion of detection systems. The threshold of "any major US platform" rather than "all platforms" provides multiple paths to resolution, moderately increasing probability, but major platforms have competitive incentives to maintain user trust through authenticity signals.Key uncertainty
The speed of improvement in synthetic media detection evasion versus platform detection capability development over the next 18 months—if AI generation becomes trivially easy to disguise while detection stagnates, the 50% threshold becomes much more likely; conversely, if detection advances faster than generation evasion, probability drops substantially.