AI Stocks Drive 80% of S&P 500 Gains as Earnings Growth Outpaces Valuations

Artificial Intelligence Stocks Dominate Market Performance

Artificial intelligence-related equities have powered more than 80% of the S&P 500's returns through 2026, according to new analysis from Jefferies that addresses growing concerns about whether this concentrated rally represents sustainable growth or dangerous speculation.

The investment bank's research suggests the AI sector's momentum stems from genuine earnings expansion rather than inflated valuations, a distinction that could determine the rally's longevity. Without AI companies contributing to performance, the broader S&P 500 index would show gains of merely 2% for the year.

Earnings Momentum Justifies Stock Performance

Jefferies' quantitative strategy team, headed by Desh Peramunetilleke, found that forward earnings projections for AI-focused companies have surged over 30% since the middle of 2025. Current analyst consensus forecasts indicate these firms could achieve a compound annual earnings growth rate of 38.5% across 2026 and 2027.

This growth trajectory significantly outpaces the 11.9% earnings expansion expected for non-AI sectors over the same period. Despite this outperformance, AI stocks trade at approximately 25 times forward earnings—a multiple that remains below historical one-standard-deviation levels.

The sector's price-to-earnings-growth (PEG) ratio of 0.6 times leads Jefferies to characterize artificial intelligence as "the cheapest sector to own in the U.S." when evaluated on this metric.

Sector Performance Shows Distinct Patterns

Performance within the AI ecosystem has varied considerably across different industry segments. Companies operating in AI server infrastructure, optical components, and memory technologies have generated the strongest returns during 2026.

Meanwhile, hyperscale cloud providers and semiconductor design companies have lagged behind other AI subsectors. Jefferies' analysis indicates memory and compute-focused stocks currently offer the most attractive valuations based on PEG ratios, while semiconductor equipment makers and chip designers appear relatively expensive.

Recent Earnings Results Support Optimistic Outlook

The latest quarterly reporting period reinforced positive sentiment around AI investments. Approximately 86% of companies exceeded analyst earnings expectations—the highest beat rate since the post-pandemic recovery period and an improvement from the previous quarter's 75% rate.

Revenue performance also strengthened, with 82% of companies surpassing forecasts. However, Jefferies observed that earnings beats outside the AI sector haven't consistently translated into stock price gains, while companies missing estimates faced significant selling pressure.

"Beats were followed by upgrades, suggesting earnings risks are low despite the geopolitical uncertainty," the strategists noted.

Management Confidence Remains High Despite External Pressures

Corporate leadership maintains an optimistic tone despite ongoing geopolitical tensions. Analysis of approximately 330 earnings calls through AlphaSense revealed that 95% of management commentary carried positive sentiment.

Analyst sentiment also improved, with 58% of earnings calls reflecting positive outlooks compared to 48% during the fourth quarter of 2025.

The ongoing U.S.-Iran conflict emerged as a notable concern, with 44% of companies identifying it as a negative factor. Executives specifically highlighted supply chain disruption risks and weakening consumer confidence as primary issues stemming from geopolitical instability.

Broader Market Shows Limited Growth Outside AI

Earnings momentum beyond artificial intelligence and commodity sectors remains constrained. Jefferies calculated that aggregate S&P 500 earnings revisions over the past three months totaled approximately 6%, but this figure drops to just 0.3% when excluding AI and commodity-related businesses.

This disparity underscores the market's current dependence on AI sector performance and raises questions about whether broader economic growth can eventually support more diversified market gains. The concentration of returns in a single theme, while currently justified by fundamentals, presents both opportunity and risk for investors navigating an increasingly specialized market environment.