AI infrastructure capex surge lifts mega-caps; valuation stretch tests support at SPY resistance

The artificial intelligence infrastructure buildout continues to accelerate, with Meta committing $21 billion to CoreWeave for long-term inference capacity, Cerebras raising $5.55 billion in its IPOInitial Public Offering - a company's first public sale of stock., and Nvidia capturing the bulk of demand for H100 and H200 GPUs. These announcements have reignited mega-cap outperformance, with NVDA, MSFT, and META leading the S&P 500 higher and pushing the Nasdaq toward fresh record highs. However, the concentration of returns into a handful of names is creating fragility: top 10 stocks now represent a material percentage of index returns, leaving breadth vulnerable if sentiment shifts.

The narrative rest on a bedrock assumption: that AI capex will sustain at current run rates and generate sufficient returns on invested capital to justify valuations. CoreWeave's multi-billion-year commitments from hyperscalers like Meta and others suggest conviction on the ROI side. However, some market commentators have begun questioning whether the capex cycle has peaked relative to revenues generated. Goldman's recent forecast adjustments and RBC's warnings about industrials and equities being stretched valuations suggest that consensus is starting to price in a more cautious growth scenario.

Meanwhile, broader market breadth is deteriorating. Retail sales data helped equities rally earlier this week, but the move has been narrow. Small-cap indices like the Russell 2000 have lagged, and breadth indicators are showing divergence. Samsung's selloff and spillover into US tech futures earlier this week illustrated how Asia supply-chain shocks can ripple into mega-cap sentiment, even if Nvidia's gross margins remain intact.

Bulls argue that AI capex is transitional and justified by long-term productivity gains; a multi-year cycle, not a one-year phenomenon. Bears counter that valuations have moved too far ahead of actual earnings accretion and that concentration risk is now a systemic feature of the market, vulnerable to any growth disappointment or macro shock. The fact that BofA strategists are flagging June as ripe for profit-taking suggests that even bulls acknowledge the need for a breather after the weeks-long rally.