Human traffic—monetised with ads—is the economic fuel of much of the internet. A steady flow of traffic is also needed to build online communities. Wikipedia, whose visitor numbers have fallen by 8% in the past year by one measure, warns that AI summaries without attribution could deter people from contributing. Stack Overflow, a coding community whose traffic has more than halved, reports that fewer questions are being asked on its chat boards. Reddit, another giant forum, saw its share price fall by half earlier this year over concerns about bumpy search referrals.