"We believe the move validates GOOG's strong fundamentals and provides Berkshire exposure to a leading AI provider through Google Cloud and Gemini expansion," Angelo Zino, an equity analyst at CFRA Research, wrote in a note on Monday. "The endorsement likely bodes well from an investor confidence perspective."

The timing of the disclosure arrived at a tricky moment for Big Tech and the widening array of companies investing in artificial intelligence.

Wedbush analyst Dan Ives summed it up as a "mini-panic moment," as investors question sizable valuations and second-guess themselves amid growing debate around an AI bubble. Mohamed El-Erian, chief economic adviser at Allianz, has called it a "rational bubble." When the possible payoff is so big, the thinking goes, it doesn't make sense to sit out. Besides, impressive, broad-based earnings have served as a critical anchor for the market, validating high expectations.

But narratives, and the investor sentiment that drives them, can change quickly.

It's worth emphasizing that all the tech giants wielded cash-generating, genre-defining operations well before the turn to AI. But Google's more modest valuation sets it apart, combined with healthy revenue growth and the cash flow potential from its core advertising business. Perhaps, as Zino noted, those traits made Google a more comfortable AI play for Berkshire.

Warren Buffett's perceived validation continues a win streak for Google. The stock is up more than 50% for the year, claiming the prize of the best-performing "Magnificent Seven" name so far. It says something too that Berkshire continues to trim its top position — Apple — as its disclosure shows.