The 10 largest companies in the S&P 500 account for about 40% of the index’s total market capitalisation, well above the 27% peak reached during the 1999–2000 tech bubble. Allianz chief investment officer Ludovic Subran called SpaceX’s $25bn bond sale shortly after an $86bn listing a signal that markets were entering bubble territory. Jeremy Grantham said the AI bubble was about to burst and he was selling up, while BCA Research’s Dhaval Joshi described the situation as ‘madness of crowds’. The S&P 500 had surged in late March after Donald Trump announced talks with Iran, reversing a brief sell-off following missile launches in February. The piece argues the bubble has further to run because the top firms are making huge profits, the US president is willing to lose wars to keep markets happy, and the world is awash with savings looking for a home.