The five largest technology companies in the world are spending $700 billion in 2026 alone on artificial intelligence infrastructure. The cumulative four-year buildout approaches $1.5 trillion. It is the largest private infrastructure investment in the history of capitalism. And the money to pay for it does not yet exist. OpenAI's $20 billion in annual revenue represents three percent of what the hyperscalers are spending to build the infrastructure around it. GPU utilization rates sit below 70 percent at three-quarters of organizations surveyed. Rental prices for the most sought-after AI chips have collapsed 64 percent from their peak. Satya Nadella, the CEO of Microsoft, has said publicly: "There will be an overbuild." Alibaba's chairman told a summit audience he was starting to see "the beginning of some kind of bubble." They are both still building. The financing behind this bet is invisible. Moody's has identified $662 billion in future data center lease commitments that do not appear on any balance sheet, equal to 113 percent of the Big Five's combined reported debt. Meta built a $27 billion data center campus through an off-balance-sheet entity called Beignet Investor LLC, funded by PIMCO, BlackRock, and Apollo, with the debt kept entirely off Meta's books. Morgan Stanley projects $800 billion in private credit data center financing over the next two years, much of it through short-term construction loans that must be refinanced starting in 2027. The pipeline runs from GPU cluster in Northern Virginia to pension fund in Scranton, with multiple layers of leverage and opacity in between. Meanwhile, data centers are consuming 183 terawatt-hours of electricity per year. Constellation Energy is restarting Three Mile Island, the site of America's worst nuclear accident, under a 20-year deal with Microsoft. Communities across the country are blocking projects at four times last year's rate. And the transformer shortage means the grid physically cannot deliver the power the industry is demanding. This has happened before. In the late 1990s, the telecom industry spent $500 billion laying fiber-optic cable on the assumption that internet traffic was doubling every 90 days. The assumption was wrong. Eighty-five percent of the fiber went dark. WorldCom filed the largest bankruptcy in American history. Bond investors recovered twenty cents on the dollar. The fiber eventually lit up. It took a decade. The investors who built it were bankrupt. The companies that bought the wreckage for pennies, Amazon and Google among them, built empires on it. Dark Fiber tells the story of the largest bet in the history of private enterprise: who is making it, how it is being financed, where the risk is hiding, and what happens if the revenue doesn't come. Drawing on primary sources from Moody's, Morgan Stanley, the International Energy Agency, Quinn Emanuel, and dozens of corporate filings and regulatory reports, this is the book about the risk underneath the AI boom that nobody is writing and everyone should read. From the bestselling author of The Shadow Lenders, The Last Ounce, and The Slow Fuse.