The largest technology companies are betting on an AI future powered by gigantic data centers filled with humming servers.

Now that the staggering cost of this push is coming into sharper focus, it’s testing nerves on Wall Street.

Three bellwethers from different corners of the technology world – Alphabet Inc., Meta Platforms Inc. and Microsoft Corp. — together racked up some $78 billion in capital expenditures last quarter. That’s up 89% from a year earlier.

Most of that cash was destined for data center construction and graphics processing units and other gear to fill them. Each increased their forecasts for future outlays. That was enough to rattle investors conditioned to expect enormous spending.

Meta shares slid 8.3%, and Microsoft was down 2.7% in early trading on Thursday following the companies disclosures of their expenditures as part of quarterly reports. Meta warned that 2026 spending would be “notably larger” than in 2025.

Though Google investors largely took its capital increase in stride, sending the shares up more than 7% in premarket trading, the trio of reports renewed questions over whether a bubble is forming.

On a conference call with Microsoft executives, Bernstein analyst Mark Moerdler asked if they were confident that the AI investments would pay off. “Or, frankly, are we in a bubble?”

Microsoft Chief Financial Officer Amy Hood reiterated that the company can’t meet current demand for AI and other services, even after spending tens of billions in recent quarters. “I thought we were going to catch up,” she said. “We are not. Demand is increasing. It is not increasing in just one place. It is increasing across many places.”

Read More: Microsoft’s Data Center Crunch Persists Despite Heavy Spending

Microsoft helped kick off the artificial intelligence boom by backing OpenAI with a $13 billion investment. And the software giant’s data center build-out is seen as key to maintaining leadership in the AI field.

Still, the company surprised investors by notching a record $34.9 billion in capital expenditures during the September quarter.

The Azure cloud-computing division – Microsoft’s main vehicle for recouping those investments – saw revenue continue to rise at a rapid clip, but at about the same rate as the prior quarter. A higher growth rate would have provided more assurance that the spending binge is worth it.

Alphabet’s Google, meanwhile, gave a more encouraging outlook. The company said its Gemini AI assistant now has 650 million monthly active users, up 44% from three months ago. And the Google cloud platform has bagged more billion-dollar deals in the first nine months of 2025 than in the prior two years, CFO Anat Ashkenazi said on a call with analysts.

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Cloud revenue rose 34% to $15.2 billion, beating the $14.8 billion estimate. But Google’s expenses also are climbing. The company expects its capital expenditures to be as much as $93 billion this year, up from the previous estimate of $85 billion, Ashkenazi said. Next year, she sees a “significant increase” in those numbers.

Investors will get a clearer picture of the cloud computing industry on Thursday, when market leader Amazon.com Inc. is scheduled to post its results. Apple Inc. also is slated to give its quarterly numbers that afternoon.

Of the three companies reporting on Wednesday, Meta offered the most jarring picture. In addition to posting an eye-popping $16 billion tax charge, the company warned that capital spending would grow at a “significantly faster” clip next year.

Unlike Microsoft and Google, Meta isn’t a major cloud-computing provider to outside customers. That means its spending spree could be riskier.

If Microsoft and Google overestimate the need for AI services, they already have a way to sell excess computing power to others. And that external demand remains healthy. Both companies reported enormous increases in their backlogs — a tally that represents what customers have committed to spend in the future.

Microsoft’s backlog for commercial customers, which includes some non-cloud expenditures, was $392 billion. Google’s was $155 billion, almost double where it stood just 18 months ago.

With Meta, the AI payoff is less clear. The company, which is infusing AI services into Instagram and Facebook, said the investments will help it better target advertising. That’s the main source of revenue for the Menlo Park, California-based company.

During Meta’s earnings call Wednesday, Chief Executive Officer Mark Zuckerberg said the company has options if it ends up spending too much on infrastructure. In one scenario, he said, the company could use the extra computing capacity for its core business. In another, it could sell the power to other companies.

“We haven’t done that yet,” he said. “But obviously, if you got to a point where you overbuilt, you could have that as an option.”

Read More: Meta’s Higher Spending in Pursuit of AI Payoff Shakes Investors

The company also faces concerns about spending in its Reality Labs division, which makes AI smart glasses and other wearable devices. The business reported a loss of $4.4 billion for the third quarter, with revenue of just $470 million.

Still, smart glasses are a “huge opportunity,” Zuckerberg said. And the broader danger in AI is spending too little, not too much, he argued.

“I think it’s pretty early, but I think we’re seeing the returns in the core business,” he said. “That’s giving us a lot of confidence that we should be investing a lot more, and we want to make sure that we’re not underinvesting.”