NVIDIA's latest 13-F filing also indicates it sold its stake in Serve Robotics, and shares of the self-driving-technology company are also sliding.

Many investors hadn't heard of SoundHound AI Inc. before a year ago, when Nvidia Corp. filed its first 13-F form, which showed a position in the maker of voice-based artificial-intelligence technology.

SoundHound shares (SOUN) surged some 570% in the year through Thursday's close, as investors took a closer look at the company's potential to win more AI partnerships.

From the archives (February 2024): Nvidia discloses positions in SoundHound AI, Arm - and these other stocks

But shares were falling 25% in Friday morning action after Nvidia's latest 13-F no longer showed a position in SoundHound as of the end of the December quarter.

Nvidia declined to comment on the filing. SoundHound didn't immediately respond to MarketWatch's request for comment.

Quarterly 13-F forms are required for investors that "exercise investment discretion over $100 million," according to the Securities and Exchange Commission. While these forms typically come from professional investment managers, they can also come from companies that hold significant investments in public companies.

Nvidia owned 1.7 million shares of SoundHound, valued at just over $8 million, as of its September 13-F.

Though SoundHound's stock is down following the latest filing, the company could continue to capture investor attention even without the Nvidia tie. SoundHound is expected to post $84 million in revenue for 2024 but was valued at $5.6 billion prior to Friday's selloff, suggesting the stock has become a broader speculative bet on future AI winners.

Wedbush analyst Daniel Ives called SoundHound "a long-term winner in the AI revolution" in a note to clients last December.

Nvidia also owned 3.7 million shares of Serve Robotics Inc., a maker of self-driving delivery technology. The shares were valued at $29.6 million at the end of the September quarter. That position is gone as well from Nvidia's latest 13-F for December.

Serve Robotics shares were taking an even steeper Friday morning dive, off 40%. Nvidia's Serve position represented 8.4% of the shares outstanding, and Nvidia was the second-largest shareholder, behind Uber, according to FactSet data.

Serve Robotics didn't immediately respond to a MarketWatch request for comment.

Nvidia's latest filing also shows a pruning of its stake in ARM Holdings, the hot chip-design stock. Nvidia owned 1.1 million shares as of Dec. 31, whereas it owned nearly 2 million shares as of Sept. 30.

Arm's stock is down 5% in Friday morning action. Nano-X Imaging Ltd. fell 13%.

The 13-F newly shows stakes in WeRide Inc., a Chinese autonomous-driving company, and NEBIUS, an AI-infrastructure company. However, 13-F filings are not always clear indicators of recent investment activity, as they can also reflect a requirement to disclose prior investments in companies that have gone public during the reporting period. For instance, WeRide went public during the December quarter and said in its prospectus that Nvidia became an "early-stage investor" in 2017. Nebius saw its trading resume in October after it had been suspended in 2022 related to its ownership of Russian assets that have since been divested.

Still, Nebius shares are up 8% in morning trading and WeRide shares rose 66%.

The overall value of Nvidia's holdings dropped to $304.5 million from $432.9 million the previous quarter.