Citi Research's August 1st report reveals AI-related stocks comprise 48.4% of S&P 500 market cap. Despite 95th percentile P/E valuations, PEG ratios remain reasonable. The study introduces "Earnings Sharpe Ratio" - AI stocks score 0.74 vs non-AI tech's 0.38. Core thesis: current "bubble vs bull paradox" leans toward structural bull market. AI infrastructure build-out expected to continue 1-2 years, requiring eventual handoff to AI adopters. Investors should focus on valuation reasonableness, operational efficiency gains, and transition timing.