- The S and P 500 has gained 93% since ChatGPT was released on November 30, 2022, adding roughly $33 trillion of market value. Nearly three-quarters of that came from 20 companies, most of them in the AI business, according to Bloomberg reporting.
- Nvidia is the largest single contributor by a wide margin, having risen 1,300% and accounted for about 16% of the index gains over that span. Anyone holding an S and P 500 fund has therefore been buying a concentrated technology position without choosing one.
- Bloomberg estimates that half of the 2% US GDP growth over the past year was driven by AI-related investment. That means the exposure extends past the equity allocation into the broader economy that bonds, property and employment depend on.
- The average defined-contribution plan held 75% in stocks as of 2025 according to Vanguard, leaving 25% in bonds, cash and other assets. Those bond holdings are themselves under pressure from a Federal Reserve that raised rates last week and may do so again this year.
What Happened?
Two developments have made analysts uneasy about the concentration. The first is the push to slow AI development, proposed by the leaders of Anthropic and OpenAI after employees at both firms resigned saying models were advancing too quickly without adequate safeguards. The second is rising interest rates, which raise the cost of the borrowing large technology companies rely on to fund the AI buildout. Institutional investors and pension managers have told Bloomberg that the breadth of the AI boom has turned the diversification they normally depend on into an illusion. Separately, retail investors are entering private markets to buy into Anthropic before a listing expected this autumn, accepting high fees, lockups, volatile fund prices and opaque ownership structures. Anthropic is projected to reach the Nasdaq at a $2 trillion valuation, and its IPO has reportedly slipped from October to November. SpaceX debuted above $1 trillion.
Why It Matters?
The GDP figure is the one that changes the analysis, and the column does not quite follow it through. If half of US growth is AI investment, then the standard remedies for equity concentration do not work as advertised. Bonds price off an economy that AI capital spending is holding up. Commercial property demand, particularly in the data centre and power markets discussed elsewhere, is directly downstream of the same spending. Employment in construction, utilities and professional services increasingly depends on it. Adding bonds and real estate to a portfolio heavy in AI equities reduces correlation on paper while leaving the underlying dependency intact. Genuine diversification here means assets that would benefit from, or at least survive, a slowdown in AI investment, and those are scarcer and less comfortable to hold. The retail rush into pre-IPO Anthropic exposure is the behaviour worth flagging most directly. Investors whose index funds already carry heavy AI weight are adding illiquid, high-fee, hard-to-value exposure to the same theme, and describing it as accessing private markets does not make it diversification. It is the same bet with worse liquidity and less price transparency. The honest counterweight is that this concentration has produced extraordinary returns and that exiting early has been costly. The point is not to sell but to know what is actually held, since someone who believes they own a diversified index fund and a bond sleeve may own one position expressed three ways.
What Next?
Anthropic listing, now expected in November rather than October, is the concrete event and a $2 trillion debut would add a second enormous AI weight to the index, further concentrating passive portfolios. Watch whether the slowdown discussion produces any actual reduction in capital spending commitments, since that is what would connect the safety debate to the GDP figure. The Federal Reserve October and December meetings matter because further increases raise the borrowing costs funding the buildout. For individual portfolios the practical step is to check what proportion of total equity exposure sits in the top 20 names across all funds held, including target-date and total-market funds, as the overlap is usually larger than investors expect. Anyone holding pre-IPO vehicles should confirm the lockup terms and what the fund actually owns before the listing rather than after.
Affected Tickers: NVDA
Source: Bloomberg
