When a company gets dropped? Index funds have to sell. That creates selling pressure, often sending the stock lower.

But beyond the mechanical buying and selling, inclusion in the S&P 500 is a signal. It says: this company is now large and important enough to represent the U.S. economy. It attracts more analyst coverage, more institutional ownership, more credibility.

And what companies S&P Dow Jones Indices chooses tells you what they think matters going forward.

The AI Infrastructure Story

Three of the four additions are AI infrastructure plays. That's not a coincidence.

Vertiv makes the cooling and power systems that data centers desperately need as AI workloads explode. These servers run hot—literally—and if you can't cool them efficiently, you can't run them at all. Vertiv is benefiting from every company racing to build AI capacity.

Lumentum and Coherent are both in the semiconductor supply chain. Lumentum does optical networking components—the stuff that moves data at light speed inside data centers. Coherent provides materials and lasers critical for chip manufacturing.

The S&P 500 is basically saying: we think the AI infrastructure buildout is real and sustained enough that these suppliers deserve to be in the index.

What About Consumer Discretionary?

Notice what's not getting added: consumer-facing businesses. And notice what's getting kicked out: Match Group (dating), Lamb Weston (fries).

That tells you something about where the economy is headed. When consumer spending is under pressure—gas prices spiking, inflation still elevated, job growth negative—companies that rely on discretionary spending struggle.

Meanwhile, B2B infrastructure companies selling to corporations and cloud providers? They're thriving, because those customers have deep pockets and AI spending is still a priority.

The March 23rd Effect

Keep an eye on these stocks around March 23rd. You'll likely see the four additions pop as index funds buy. You'll likely see the four deletions drop as index funds sell.

But the more interesting question is: six months from now, will these companies still be outperforming? Index inclusion isn't a guarantee of success—it's a snapshot of where the market is right now.

If AI infrastructure spending stays strong, Vertiv, Lumentum, and Coherent will keep doing well. If the AI buildout slows or hits a rough patch (like, say, Oracle and OpenAI cancelling data center projects), these stocks could struggle.

What This Means for Your Portfolio

If you own an S&P 500 index fund—which most people do in their 401(k)s—you're about to automatically own more AI infrastructure exposure and less consumer discretionary exposure. You didn't make that choice; the index did it for you.

That's fine if you agree AI infrastructure is where the growth is. But if you think the sector is overheated, you might want to rebalance.

The key takeaway: index funds aren't neutral. They're making active bets based on what companies qualify for inclusion. And right now, those bets are tilted heavily toward tech infrastructure and away from consumer discretionary.

Understand what you own. Because even "passive" investing has an active tilt baked in.