Big Tech's AI capex surge is creating a dramatic cash flow squeeze, with Microsoft, Amazon, Alphabet and Meta spending $165 billion in Q2 against just $7 billion in free cash flow. According to Jefferies' Global Head of Equity Strategy Christopher Wood, consensus forecasts show the four hyperscalers' aggregate free cash flow falling to negative $12 billion in Q3, marking a dramatic reversal from the $60 billion generated in Q4 2025. The free cash flow generation of the S&P 500 has begun to deteriorate, with the index's free cash flow yield falling to 2.65% from 4.76% in October 2022, though it remains above the recent low of 2.50% reached in October 2025. The quartet accounts for 17.7% of the S&P 500, making their cash generation erosion a broader market issue.
The more concealed risk lies in who is underpinning the expected returns from Big Tech's massive AI investments. OpenAI and Anthropic account for an estimated 45% to 50% of Amazon's contracted revenue backlog, about 40% of Google's and 30% to 40% of Microsoft's, according to Jefferies' US technology analysts. OpenAI and Anthropic accounted for roughly 45% of Google Cloud Platform revenue in Q2 and about 25% of Microsoft Azure revenue, with their contribution to Amazon Web Services lower at roughly 6% but expected to rise to 12% to 18% in Q3. The exposure is significant because the AI laboratories are cash-burning customers, potentially making them riskier counterparties than traditional corporate cloud clients. AI-related services generate only about 15% of their cloud revenue, with traditional cloud services supplying the remaining 85%.
The structural concentration in the S&P 500 reveals unprecedented market dependency on AI-related investments. J.P. Morgan Global Research estimates that the top 20 stocks now account for roughly 50.8% of total market capitalization, with no modern precedent for such heavy dependence on so few companies. This concentration means that buying the market increasingly means buying the AI trade, regardless of performance from the remaining 480 companies. The Vanguard S&P 500 ETF (VOO) has reached $1.03 trillion in assets, becoming the first ETF to cross the trillion-dollar mark while charging just 0.03% in fees, significantly lower than the SPDR S&P 500 ETF Trust (SPY) which charges 0.0945%. Galloway warns that 'if that slows, the U.S. would plunge into a recession immediately'.
Despite massive AI investments, the financial benefits are not yet widespread across industries. Torsten Sløk, chief economist at Apollo, notes that net profit margins for the technology and communications services sectors have gone up since the end of 2022, when OpenAI introduced ChatGPT. However, margins for numerous other sectors, such as healthcare, consumer staples, energy and materials, are either flat or down over the same period. According to Sløk's data, net margins for the Magnificent Seven are hovering around 25%, up from about 15% in late 2023, compared with about 10% for the so-called Other 493 companies in the S&P 500. Sløk warns that the AI capex boom is so far only showing up in the sellers' margins, not the buyers', creating significant downside risks as the S&P 493 companies haven't yet generated returns on their AI investments. Sløk expects margins to eventually expand in sectors outside tech and telecom services, but the speed at which this happens is key for markets.
Recent market performance has delivered stress tests for AI-focused investments, with the Nasdaq falling almost 10% from its June peak by late July before staging a near-9% rebound in early August. According to TradingView data, momentum names showed particular fragility, with Sandisk and Western Digital, up roughly 396% and 145% year-to-date, both displaying sell-the-news vulnerability during earnings season. However, the bull case remains supported by strong fundamentals, with Goldman Sachs finding 64% of reporting S&P 500 companies beat consensus earnings by at least a standard deviation. The Situational Awareness hedge fund collapse in July serves as a cautionary case study, with the fund growing to $45 billion before steep losses on AI infrastructure stocks forced it to sell its entire portfolio. Despite growing concerns, institutional bodies maintain mixed perspectives, with BlackRock rejecting the bubble framing and arguing that today's leaders generate real profits, though whether returns eventually justify trillions in capital expenditure remains critical for the entire index's sustainability.
