Nvidia regained its title as the world's most valuable company Friday after Apple stock slumped and Amazon.com reminded everyone how important Nvidia's processors are to the artificial-intelligence boom.

Nvidia shares closed up 2.9% at $200.75, raising its market cap to $4.86 trillion. Apple, which briefly held the crown, saw its market cap fall to $4.51 trillion following the iPhone maker's sharp drop after its earnings Thursday. Its shares fell as low as 10% in intraday trading Friday, but pared some of those losses by the end of the day.

Meanwhile, Amazon played down competition between its custom AI chips and Nvidia's processors. It also raised its capital expenditure forecast for the year to $220 billion from $200 billion.

"We...continue to have a deep partnership with Nvidia and will continue making AWS [Amazon Web Services] the best place to run Nvidia chips, as we have customers who will run on Nvidia for as long as we can foresee," said Amazon CEO Andy Jassy in an earnings call.

The comments aren't exactly new. Jassy said last year that the online retailer-and-cloud computing company had a "very deep relationship with Nvidia" and would be buying its chips for the foreseeable future. Still, Nvidia shareholders have braced for a less amicable relationship, amid reports Amazon is set to start selling its Trainium AI chips directly to customers.

"We do have an increasing number of customers who are interested in us providing the training and chips to them separate from our cloud," Jassy said Thursday. "We're actively having those conversations and exploring. And I expect there's a real chance we'll do that in the future."

The custom AI chip threat isn't going away for Nvidia. But at least for now, it's still the biggest in the business.