The AI trade still has room to run, but the warning sign to watch is the moment companies can no longer raise cash — bad news for investors when it flips, fine for now.

• The dot-com crash came when the money window slammed shut and cash-burning internet firms could not raise more.
• Tech is now 36% of the whole US stock market, and Microsoft plus Nvidia alone match the entire size of the old internet bubble.
• Microsoft owes more this year than it has in cash, so it has to lean on incoming profits instead of buybacks or paying down debt.
• CoreWeave has 18 billion in bills against 10 billion in cash, yet investors just piled into its new debt raise — proof the party is still going.
• Anthropic delaying its IPO, with OpenAI waiting behind it, is the first small crack worth watching.

Outlook: The next real test is SpaceX's coming fundraise — strong demand means the boom continues, weak demand means the top is in.