Stock bull market nears 4-year anniversary driven by AI spending — but there are looming risks

• Nvidia's market cap has surged from $286 billion to $5.8 trillion since October 2022, with the top 10 S&P 500 companies now representing 40% of the index versus 28% four years ago, creating significant concentration risk
• Oxford Economics estimates one-third of recent US economic growth stems from AI-related investment and wealth effects, with only technology and communication services sectors outperforming the broader index during this bull run
• Rising 10-year Treasury yields hovering around 5.2% (highest in 24 years) and Fed rate hikes present headwinds, making bonds increasingly competitive with equities and potentially slowing economic growth

Summary: US Stock Bull Market Approaches Four-Year Mark Amid AI Boom and Growing Risks

The US bull market is approaching its four-year anniversary on October 12, marking the period since the S&P 500's cycle low. The benchmark index is trading near record highs, delivering a 117% gain—the sixth-best performance among post-WWII bull markets and currently the eighth-longest run.

Key Driver: AI Investment

Artificial intelligence spending has been the primary catalyst, with ChatGPT launching just one month after the bull market began. Oxford Economics estimates AI accounts for approximately one-third of recent US economic growth through infrastructure investment and wealth effects. S&P 500 earnings are expected to surge over 35% this year, driven largely by hyperscaler capital spending on data centers.

Market Performance

Technology and communication services sectors have outperformed the broader index. Nvidia exemplifies this AI boom, with its market capitalization soaring from $286 billion to $5.8 trillion since October 2022, making it the world's largest company. Thirteen US companies now exceed $1 trillion in market value, nearly all with significant tech or AI exposure.

Mounting Risks

• Concentration concerns: The top 10 S&P 500 companies now represent 40% of index weight, up from 28% in October 2022
• Interest rate pressures: Federal Reserve rate hikes and the 10-year Treasury yield hovering around 5.2% (24-year high) create headwinds
• AI dependency: Any weakness in AI spending could trigger sharp corrections
• Election volatility: Upcoming midterm elections may increase market turbulence

Strategists note that while fundamentals remain solid, the "easy money" in AI has been made, with increasing pressure on tech companies to convert spending into profits.