A handful of AI-dependent tech giants now dominate retirement index funds, and cracks in their business model could trigger a 2008-style wipeout for everyday savers.

• Seven companies (Amazon, Apple, Microsoft, Meta, Tesla, Nvidia, Alphabet) make up a third of the S&P 500, so 401(k) index funds are far less diversified than people think.
• Top AI labs like OpenAI are losing tens of billions a year while Big Tech piles on debt to build data centers, betting on future AI profits that haven't shown up yet.
• China's free, open-source DeepSeek model undercut the idea that premium AI would always command high prices, already wiping out huge market value from Nvidia and other chip and tech stocks.
• If AI company valuations keep slipping, automated selling in index funds could cascade, and since those same tech stocks underpin confidence in US bonds, a sell-off could even make it harder for the government to borrow.
• Unlike 2008, falling interest rates may not be able to fix this bubble because the AI spending binge is tied to revenue promises that may simply never materialize.

Outlook: Expect continued volatility in AI-linked tech stocks, with retirement savers heavily exposed if the sector's spending outpaces real profit growth.