Alphabet (GOOGL) experienced its worst single-day performance in history on October 29, with shares falling approximately 13% and wiping out roughly $500 billion in market value. The primary driver was a miss in free cash flow, which reported at minus $9.07 billion due to heavy AI spending, contrasting sharply with analyst expectations for a positive number. A senior executive explicitly attributed weakness in search ad revenue to the rollout of 'AI Mode,' noting that users receiving direct answers within the chat interface are clicking fewer ads and links. The article details how Google's strategic pivot toward AI-generated answers is fundamentally altering its traffic dynamics, directly impacting its core advertising business model. While Google plans to integrate ads and shopping suggestions directly into the AI conversation to mitigate revenue loss, the immediate financial impact has been severe. This shift represents a significant structural change for Alphabet, as the traditional 'rank on Google and wait for clicks' strategy is weakening, forcing a re-evaluation of how search traffic is monetized. Beyond Alphabet's internal struggles, the broader AI sector faces scrutiny over spending efficiency and capacity constraints. Competitors like OpenAI adjusted their fundraising targets downward, while Microsoft trimmed its capital expenditure forecast due to chip supply delays pushing new capacity into 2027. Meanwhile, Google continues its aggressive investment plan with capex between $195 and $205 billion. The market reaction suggests investors are questioning the immediate return on these massive AI investments, particularly as traffic referral issues affect partners like Reddit.