The S&P 500 Is Near 7,800 — And Without AI Stocks, the Rally Barely Exists

The S&P 500 closed at 7,646.04 on September 18, 2026, sitting about 152 points below its all-time high of 7,798.99 set in August. The index has closed at a record 27 times so far in 2026 and is up roughly 13% year-to-date (Yahoo Finance). But the real question hanging over the market isn't whether it will keep setting records — it's how narrow the rally actually is underneath the headline number.

The Rally Is Almost Entirely About AI

Strip out AI-related stocks, and the picture changes dramatically. From May 2024 to June 2026, the S&P 500 posted a 142% gain — but removing AI stocks from that calculation collapses the return to just 16%. AI stocks now account for roughly 45% of the S&P 500's total market capitalization, an all-time high for any single thematic cluster within the index (Northwestern Mutual). That's the clearest evidence yet that the index's headline gains reflect a small handful of companies riding the AI infrastructure buildout rather than broad-based corporate strength.

Market Breadth at Its Narrowest Since the Dotcom Era

The concentration shows up starkly in breadth data: fewer than 30% of S&P 500 constituents actually outperformed the index itself during the second quarter of 2026 — one of the narrowest breadth readings since the dotcom bubble (Morgan Stanley). When the vast majority of stocks in an index are lagging the index's own return, it means a small number of mega-cap names are doing nearly all the work, which is exactly the kind of concentration risk that historically precedes sharper-than-average drawdowns when sentiment shifts on the leading names.

What's Actually Supporting the Rally

It's not pure hype, though. Earnings growth has been genuinely strong — blended S&P 500 earnings per share grew almost 30% year-over-year in the most recent quarter — and semiconductor stocks specifically rose 55% in the quarter, with hardware up 29%, together contributing nearly 60% of global equity index returns during the period. A partial easing of Middle East geopolitical risk also supported sentiment at points during the year, though that risk has proven far from resolved given the US-Iran conflict's repeated escalations throughout 2026.

Is This a Breakout or a Bubble in Waiting?

The honest answer is that both things can be true at once: the AI infrastructure buildout is producing real, substantial earnings growth for the companies at its center, which justifies at least part of the rally — but the narrowness of participation means the market's overall health is now tightly linked to a small number of companies' continued execution. If AI-related earnings growth slows or sentiment toward the sector sours, the S&P 500's headline strength could unwind quickly given how much of the gain is concentrated in so few names. That's a fundamentally different risk profile than a broad-based bull market where strength is distributed across sectors.

What This Means for Investors

Investors holding index funds should understand that a "diversified" S&P 500 position in 2026 carries far more concentrated risk than the label suggests, given AI stocks' 45% weighting. For those specifically worried about that concentration, considering equal-weighted index exposure or deliberately diversifying into the roughly 70% of constituents that haven't kept pace with the index is one way to reduce reliance on continued AI-sector strength. For those comfortable with the concentration, the earnings growth underlying the AI-driven names does provide real fundamental support — but it's worth recognizing that support rests on a narrower foundation than the S&P 500's broad-market reputation implies.

FAQ

What level is the S&P 500 actually at in September 2026? 7,646.04 as of September 18, 2026, about 152 points below its all-time high of 7,798.99 set in August, with 27 record closes so far this year and a roughly 13% year-to-date gain.

How much of the S&P 500's 2026 rally is actually driven by AI stocks? Nearly all of it by one measure — the index's 142% gain from May 2024 to June 2026 collapses to just 16% when AI stocks are excluded.

How concentrated is the S&P 500 in AI stocks right now? AI-related stocks account for roughly 45% of the index's total market capitalization, an all-time high for any single thematic cluster.

Is market breadth a concern right now? Yes — fewer than 30% of S&P 500 constituents outperformed the index itself in Q2 2026, one of the narrowest breadth readings since the dotcom era.

Is there real earnings growth supporting the rally, or is it just hype? There's genuine earnings growth — blended S&P 500 EPS grew almost 30% year-over-year, with semiconductors up 55% in the most recent quarter — but that growth is concentrated in a small number of AI-linked companies.

How can investors reduce exposure to this concentration risk? Equal-weighted index funds or deliberate diversification into the broader set of underperforming constituents can reduce reliance on continued strength from the small group of AI-driven mega-caps carrying the index.