Is AI lifting the whole S&P 500 or just its biggest names?

Capital Economics says AI-driven optimism since the launch of ChatGPT has been heavily concentrated in a handful of large-cap tech names and has lifted the S&P 500 by roughly 25% versus where it would be without that rally—implying the index might be closer to 5,000 absent the AI effect. The firm’s comparison of market-cap-weighted versus equal-weighted S&P 500 returns since end-2022 shows information technology and communication-services (and large-cap consumer discretionary) materially outperforming their equal-weighted peers, while the remainder of the index still represents more than 40% of market capitalisation. Although there is so far “no clear impact” of AI beyond big tech, Capital Economics notes adoption is widening—citing Walmart’s OpenAI tie-up—and could shift productivity and profit dynamics across the broader market over time.

Analysis

Capital Economics, via chief markets economist John Higgins, attributes a material portion of the U.S. equity rally since late-2022 to AI-driven gains concentrated in a small number of large-cap names; the firm estimates the S&P 500 would be roughly 25% lower — around 5,000 — absent that differential. Their methodology compares market-cap-weighted returns with an equal-weighted S&P 500 extrapolated from end-2022, and highlights information technology and communication services, plus large-cap consumer discretionary, as materially outperforming their equal-weighted counterparts.

The report notes that the remainder of the S&P 500 still accounts for more than 40% of market capitalization, and that there has been "no clear impact" from AI beyond the big-tech cohort to date; this suggests current gains are more about investor positioning than pervasive productivity improvements. Capital Economics flags early non-tech adoption examples such as Walmart's OpenAI partnership, indicating a potential route for AI effects to broaden if firms convert trials into measurable profit or efficiency gains.

Sentiment and market-impact signals in the article are mildly positive but cautious (sentiment score ~0.25; market-impact ~0.35), implying upside remains tied to concentrated winners and to the timing of wider corporate adoption. The divergence between cap-weighted and equal-weighted indices signals elevated concentration risk; investors should therefore monitor equal-weighted performance, corporate AI deployment announcements, and subsequent margin or revenue evidence before assuming broad-market durability.

Key Decisions for Investors

• Reduce concentration risk in top-cap AI beneficiaries by trimming outsized positions or overlaying hedges and consider exposure to equal-weighted S&P strategies to capture a broader performance base
• Monitor corporates that announce credible, measurable AI integrations (example: WMT's OpenAI tie-up) and consider selective overweight in names that can demonstrably improve margins or costs, rather than style-chasing momentum alone
• Exercise caution on undifferentiated SPY exposure given the ~25% implied AI-driven premium; consider partial hedges (options collars or inverse exposure) or a staged re-entry pending quarterly evidence of productivity gains
• Track leading indicators — divergence between cap- and equal-weighted indices, frequency and substance of AI deployment announcements, and actual earnings/margin impact — and adjust allocations only when adoption translates into quantifiable financial improvement