Alphabet shares rallied nearly 6% to a record high on Monday after Berkshire Hathaway's new stake provided an endorsement of the tech giant's artificial intelligence efforts amid heightened worries over a looming bubble.

Google stock hits all-time high as Berkshire Hathaway reveals $4 billion investment, marking Warren Buffett's rare tech bet and endorsement of AI efforts.

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.

Buffett revealed his regret missing Google after GEICO’s success—and how Berkshire’s new Alphabet investment marks a turning point in its tech strategy.

Berkshire Hathaway remains a core conservative holding, offering value amid an expensive market and robust Q3 operating results. BRK.B's diversified business model, large cash reserves, and discounted P/E versus the market provide downside protection and long-term opportunity.