One longtime tech bull is waving a white flag of sorts.

Ed Yardeni, president of Yardeni Research, has been overweight the tech sector for 15 years and often has one of the highest S&P 500 ( ^GSPC +0.06% ) targets on Wall Street. However, Yardeni is now reversing his position, going underweight on the " Magnificent Seven " stocks, and instead encouraging investors to buy the remaining 493 stocks on the broad-market index, which he dubbed the "Impressive 493."

Why Yardeni sees a shift

Yardeni's primary reason for ending his buy call on the tech sector is market concentration. On CNBC, Yardeni said that the "Magnificent Seven" now makes up 45% of the market cap of the S&P 500 , which he believes is unsustainable. He also argued that in order for those companies to continue t

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