Your retirement money may soon be funding the biggest AI companies, and some fear it's a bubble waiting to pop.

• SpaceX is leading the way, with OpenAI and Anthropic expected to go public soon too.
• Together these three could be worth $4 trillion, instantly bigger than every other US company.
• They'd leapfrog today's biggest firms basically on day one of going public.
• The worry: ordinary people's 401k retirement savings would be pouring into these stocks.
• Some warn this could become the biggest market bubble ever seen.

Outlook: If these mega-IPOs happen, huge amounts of retirement money flow into AI stocks — great if the boom lasts, painful if it pops.