New Delhi, Sept. 26 -- While Artificial intelligence (AI) spending is driving one of the most aggressive bull runs in US markets, global borkerage Jefferies has cautioned investors about growing signs of speculative excess even as gold and Chinese tech shares surge.

In its latest GREED & Fear report, Jefferies observed that the US equity rally propelled largely by AI-related capital expenditure and passive inflows has added nearly $15 trillion to the S&P 500's market value since April, an amount equal to half of America's GDP. The frenzy, however, comes amid a nearly 10 per cent fall in the U.S. dollar index this year, its weakest performance since 2017.

The report cited the euphoric reaction to Oracle's quarterly earnings as a clear in...