A big Anthropic IPO could drain money out of the stocks holding up the market, which would be bad for investors riding the AI rally.

• Anthropic is reportedly heading for a public listing at a $2 trillion value, raising about $100 billion.
• That cash has to come from somewhere, and the easiest place is the AI stocks funds already own too much of — Nvidia, Microsoft, Google, Amazon, Meta.
• Those few names are more than a third of the whole S&P 500, so selling them to buy the IPO pulls the market's main support away.
• Index funds won't automatically buy Anthropic right away, so money leaves the S&P 500 without flowing back in.
• The Fed looks set to raise rates again and oil is climbing back toward $100, adding more pressure.

Outlook: A sharp drop is expected as insiders cash out, with the pullback seen as a buying chance later.