The ‘Magnificent Seven’ are now big enough to move the economy. Why that could be a problem.

The "Magnificent Seven" — a group of large technology companies — have grown to a scale where their combined market value exceeds the entire economic output of nearly every country in the world. That concentration matters because these firms are no longer just stock market stories; their spending, hiring and investment decisions can ripple through the broader economy.

For investors, the key issue is index concentration. When a handful of companies dominate major benchmarks, broad market performance becomes increasingly tied to their fortunes. A sharp pullback in these names can weigh on diversified portfolios more than many investors expect, even if other sectors are holding up.

What to watch: whether these companies' earnings growth justifies their valuations, how regulators respond to their market power, and whether capital spending — particularly on artificial intelligence infrastructure — continues at its current pace. Any slowdown in those areas could have outsized effects, given how much of the market now rests on this small group.