Not true for Vanguard's total US stock market fund (VTSAX/VTI), the largest total US stock market fund in the world. Their CRSP index only requires 20 trading days post IPO, or 5 for large caps (this has been true for many years, this is not a recent change)

Technically they couldn't be added to the S&P 500 etc. until they become profitable.

If space x gets an exception, why wouldn't anthropic?