Everyone knows US stocks are expensive, but a fresh look shows “expensive” doesn’t do that justice. The S&P 500’s cyclically adjusted price-to-earnings ratio has crossed 40x. Correct that number for record-high earnings, and it climbs past levels seen at any point in market history. Investors are paying a premium on a premium.

• According to Bloomberg, when you strip out AI’s unusually strong earnings growth, the ratio jumps past 68 — well above both the 2000 peak (44.2) and 1929’s high (32.6).
• Market concentration also hasn’t been this extreme in decades, with the S&P 500’s 10 biggest names now controlling about 40% of the index compared to a 27% high back in 1999-2000.

The warnings pile up: Between stretched valuations and concentrated earnings, there’s little room left to absorb a slowdown. Jeremy Grantham, the 87-year-old investor who called the dot-com and 2008 crashes, says he’s selling his AI holdings, comparing the boom to railroads and the early internet — overbuilt now, profitable for only a few later. Allianz’s Ludovic Subran went further, flagging SpaceX’s $25B bond sale as proof markets have entered “bubble territory.” History says that this trade won’t last forever, but investors keep buying anyway.