S&P 500 Rally Still Driven By Megacap Tech

The numbers make the point. SPY, which tracks the S&P 500, closed at 761.69 on Sept. 18, up only modestly from 752.18 two days earlier. By contrast, MAGS — the fund that tracks the “Magnificent Seven” megacaps — has been the cleaner expression of the rally. It closed at 70.46, and while its recent move has been choppier, the long-term story is clear: the biggest tech platforms remain the market’s main engines of growth. QQQ, the Nasdaq-100 ETF, has also outpaced the broader market, finishing at 721.45, underscoring how much of Wall Street’s strength still sits in large-cap technology.

That kind of leadership is economically significant because it tells you where profits, capital spending and investor expectations are concentrated. The AI buildout continues to funnel enormous amounts of cash into the biggest cloud, chip and platform companies, while many other S&P 500 members are simply not matching that pace of earnings growth. When a market is this narrow, valuations for the leaders can stay elevated even if the broader economy is muddling through.

Adalytica’s S&P 500 Trade Signals snapshot is neutral on sentiment at 33, which fits the picture of a market that is advancing, but not with broad conviction. The 50-day moving averages for SPY and QQQ are both above their recent closes, showing the indexes are still working to rebuild momentum after a volatile summer. SPY’s relative strength index remains below 50, another sign that this is not a full-throttle breakout so much as a selective recovery led by a few heavyweight names.

For investors, the lesson is simple: don’t confuse index strength with broad market strength. If you own an S&P 500 fund, you are already heavily exposed to megacap tech whether you mean to be or not. That has worked well for years, and it can keep working if AI spending continues to translate into durable free cash flow. But it also argues for diversification beyond the usual suspects, especially if you want your portfolio to compound over the next 3 to 10 years instead of depending on one crowded trade.

The better question now is not whether megacap tech still matters — it clearly does — but whether the rest of the market can eventually catch up. Until that happens, the S&P 500 may keep making progress, but investors should remember that much of the heavy lifting is still coming from MAGS and its biggest members. That makes the index worth holding, but also worth watching closely.