Economist Steve Hanke has flagged the US stock market as being in bubble territory, citing his bubble detector and the bond-stock yield spread as confirmation signals. According to BeInCrypto, Hanke's warning comes as five mega-cap tech stocks, including Alphabet, Nvidia, Amazon, Broadcom, and Apple, have driven significant gains in the S&P 500 since April 1. These stocks contributed about six percentage points to the index's 12% rise. Additionally, call option volume on the S&P 500 reached a record $2.6 trillion, reflecting heightened risk appetite among traders.