STORY: Wall Street ended mixed on Thursday, with the Dow gaining more than half a percent, the S&P 500 flat and the Nasdaq shedding just under half a percent.Shares of major tech companies including Nvidia, Broadcom and Microsoft declined, as investors grew more finicky about AI-related stocks whose valuations have been inflated by outsized gains.Shana Orczyk Sissel, founder and CEO of Banríon Capital Management, said investors will likely become increasingly selective as the AI trade progresses."2025 started as the year of AI. 2026 is going to be more of the same, but I do think that we're going to start to see more clear winners and losers. My focus is less on the folks who are trying to build AI tools for consumers and need to monetize that technology. I'm much more interested in the companies that that are part of the infrastructure of AI, the folks who make the chips, the folks who are involved in data center development, energy efficiency at the data center level, and anything related to the infrastructure of AI."Still, shares of Alphabet gained on Thursday, a day after the Google parent surpassed Apple in market capitalization for the first time since 2019 to become the second-most valuable U.S. company. Among other stock moves, shares of defense companies gained after President Trump said the 2027 U.S. military budget should be $1.5 trillion, much higher than the roughly $900 billion approved by Congress for 2026.Shares of Northrop Grumman added more than 2%, Lockheed Martin rose more than 4%, and Kratos Defense jumped almost 14%.Traders now turn their attention to Friday's crucial nonfarm payrolls report for December, one of the first reliable economic datasets since the record-long government shutdown.