Hyperscalers are significantly ramping up their AI capex spending — and increasingly using credit markets to fund it. But investors say this shift is challenging mega-cap tech giants' so-called 'fortress balance sheet' status, and rips up what they call the "unspoken contract" that kept speculative AI spending largely separate from debt markets. After Amazon , Meta and Google-owner Alphabet all unveiled sizable increases in their full-year capex spending plans during earnings season, UBS data