Warren Buffett's favorite valuation gauge just hit a record. The so-called Buffett Indicator, which compares the total US stock market to US GDP, has climbed to roughly 232 percent, the highest level on record in GuruFocus data going back to 1970. The reading has been pushed higher by an AI-driven rally that has lifted the S&P 500 about 13 percent since the March 30 low. GuruFocus classifies any reading above 164 percent as "significantly overvalued," and its long-term model based on the current level points to slightly negative average annual returns over the next eight years or so. Buffett popularized the metric in a 2001 Fortune article co-written with Carol Loomis, calling it "probably the best single measure of where valuations stand at any given moment." Even with that warning flashing, Berkshire Hathaway under new CEO Greg Abel has been leaning into AI. Berkshire holds large positions in Apple (AAPL) and Alphabet (GOOG, GOOGL), and Abel recently committed 10 billion dollars to A...