Western Digital stock tumbled 15% ahead of the open Thursday after the hard-drive maker reported excellent quarterly earnings. The selloff points to the elevated expectations facing suppliers of the artificial-intelligence boom.

The stock had surged 201% this year ahead of the earnings print.

While the results show the continued need for data storage as part of the AI supply chain, the reaction to the company's somewhat conservative guidance indicates that investors remain wary about a potential slowdown.

Western Digital reported adjusted earnings of $3.56 a share for its fiscal fourth quarter, surpassing the $3.31 analysts had expected, per FactSet. Revenue totaled $3.75 billion, up 42% from a year ago and ahead of Wall Street's call for $3.7 billion.

Guidance was good but not great. The company expects revenue of $4.1 billion, plus or minus $100 million, and adjusted earnings per share of $3.85 to $4.15 in the current quarter. Analysts had expected revenue of $4.06 billion and adjusted earnings of $3.84 a share.

The outlook wasn't as far above forecasts as that of hard-drive rival Seagate Technology, which reported earnings last week. Seagate's guidance also implied a gross margin of over 57% next quarter, while Western Digital forecast a margin of 55% to 56%.

Western Digital pinned that discrepancy in part on quarter-to-quarter fluctuations in pricing, which should ease as old long-term agreements lapse and customers sign new agreements at higher prices.