Facebook owner Meta Platforms on Wednesday warned of a "significant acceleration" in artificial intelligence-related infrastructure expenses next year, while beating analysts' estimates for third-quarter revenue and profit.

The results sent mixed signals to investors about whether digital ad sales from Meta's core social media business would continue to cover the cost of its massive AI buildout.

Shares of the Menlo Park, California-based firm were down 2.9% in after-hours trading.

"Meta needs to prove that it can continue to cover its AI costs as they rise next year, and any weakness in its core ad business could make investors nervous as they continue to wait for a return on Meta’s bigger AI bets," said Emarketer principal analyst Jasmine Enberg.

Like its Big Tech peers, Meta has invested heavily in data centers to capitalize on the generative AI boom. Unlike providers of cloud services, however, it does not expect to earn money from those investments right away and therefore is more subject to scrutiny from investors around its spending.

Meta CEO Mark Zuckerberg acknowledged in a conference call with analysts that more infrastructure spending "is maybe not what investors want to hear in the near term," but said the company nonetheless would continue to invest.

"I just think that the opportunities here are really big," he said.

Zuckerberg added that Meta AI, a generative AI chatbot assistant that can generate images and answer questions, now has more than 500 million monthly active users. That represents a substantial jump from the 400 million users the company said were using Meta AI as of its last disclosure in September.

The world's biggest social media company kept costs in check in the third quarter, with total expenses of $23.2 billion and capital expenditure of $9.2 billion. It projected a slightly improved expense picture for the year as well, narrowing its total expense forecast to $96 billion to $98 billion.

In its press release, however, it warned of "a significant acceleration in infrastructure expense growth next year as we recognize higher growth in depreciation and operating expenses of our expanded infrastructure fleet."

Investors have been wary of Meta's spending in recent months. Its shares sank in April after it disclosed a higher-than-expected expense forecast, knocking $200 billion off its stock-market value.

That ended a run of strong quarters for Meta, which has climbed back from a share-price meltdown in 2022 by slimming its workforce, leaning in to investor excitement about AI and earlier this year issuing its first-ever dividend.

The company's shares are up around 500% from the bottom and about 67% so far this year.

On Wednesday, analysts also questioned Meta about its headcount, which stood at 72,404 employees, up from 66,185 in the year-ago quarter.

Chief Financial Officer Susan Li said Meta would focus on pushing parts of the company "to be more efficient," including those continuing to add employees.

Meta's earnings come after encouraging results from digital ad bellwethers Alphabet and Snap, which both beat third-quarter revenue estimates on Tuesday thanks in part to rising sales of AI-assisted ads.

Meta reported third-quarter profit of $6.03 per share, compared with estimates of $5.25 per share, according to data compiled by LSEG. Third-quarter revenue stood at $40.59 billion, compared with analysts' estimates of $40.29 billion.

The company also forecast between $45 billion and $48 billion in fourth-quarter revenue, compared with analysts' estimates of $46.31 billion, according to data from LSEG.

Advertising accounts for the vast majority of Meta's revenue, meaning higher marketing spend by retailers and other businesses during the holiday season could provide a crucial boost to the company's bottom line, analysts say.

Meta's family daily active people (DAP), a metric it uses to track unique users who open any one of its apps in a day, grew 5% in the third quarter to 3.29 billion. DAP increased 7% in the preceding June quarter, to 3.27 billion.

The company is well-positioned to squeeze more revenue out of users even as user growth slows, given that its AI tools can show people more content that match their interests, Enberg said.

The company's Reality Labs division, which produces its Quest virtual reality headsets, smart glasses made with EssilorLuxottica's Ray-Ban and upcoming augmented-reality glasses, lost $4.4 billion in the third quarter, narrower than analyst estimates of a $4.7 billion loss.

In thinking about Reality Labs investments for 2025, executives were excited about the progress and strong consumer interest they had seen around the smart glasses in particular, Li said.