Investors are getting increasingly uncomfortable with the amount of capital needed to make the artificial intelligence buildout a reality.

It's playing out in real time in the bond market, where the biggest names involved in the blitz — Google, Amazon and Meta — are seeing credit spreads widen as fixed-income investors demand more reward to lend to the companies.

Yields ticked higher this week after Alphabet lifted its capex forecast, raising concerns that other hyperscalers could follow suit.

Part of the reason capex budgets are going up is the rising cost of power. Energy is a major expense for all of the hyperscalers, which are constructing large data centers across the U.S. at breakneck speed.

GE Vernova CEO Scott Strazik told CNBC he expects the current inflationary environment to remain, driven in part by the heightened geopolitical backdrop. Just this week, oil broke above $100 a barrel.

The move in treasury yields is also inducing anxiety among fixed-income investors. Mizuho wrote to clients Friday morning that capex raises are testing investor limits as the companies, once seen as capital fortresses, are now seeing a dramatic rise in AI-tied costs.

The analysts added that the hyperscalers are currently on track to collectively spend more on capex than they generate in free cash flow by next year.

"It's creating intense discussions between bond and equity investors who have exposure to the biggest names in tech," said the portfolio manager of a credit fund, who asked to remain anonymous in order to discuss sensitive conversations.

As concerns grow, Oracle's 5-year credit default swap, or CDS, is once again trading at a multi-year high.

In a note to clients published on Wednesday, Barclays credit analyst Andrew Keches wrote that Oracle's CDS is once again being seen as a proxy for AI debt fears.

"The appeal of ORCL CDS in recent history has extended beyond company-specific fundamentals, reflecting its role as a liquid hedge on AI capex, OpenAI execution and broader data-center spending narratives," wrote Keches.

Oracle is facing questions from investors about how active it plans to be in the debt market in the coming years, as the buildout and leasing of data centers continue to become more capital intensive.

Earlier this month, ratings agency S&P Global downgraded Oracle's credit rating to BBB-, just one notch above junk status.

Yet executives at the company remain confident in Oracle's ability to win the AI race. The company has a growing relationship with OpenAI and hyperscalers like Meta and Nvidia, which are also working with Oracle on cloud architecture.

Still, portfolio managers who spoke to CNBC said the move in tech bond yields could impact financing future deals.

Meta is looking to finance its $12 billion Texas data center with pricing expected to be finalized early next week, according to a source familiar with the talks, who asked not to be named in order to discuss the company's plans.

The Financial Times reported that the deal will be priced at a higher borrowing rate than previous projects, a sign that investors want not only demand more, but are questioning the return on investment.