Western Digital Stock Slides Despite Strong Q4 Beat

Western Digital reported fiscal fourth-quarter non-GAAP earnings of $3.56 per share and revenue of $3.75 billion, surpassing analyst estimates of $3.29 EPS and $3.69 billion revenue. Revenue grew 44% year-over-year, reflecting strong demand in the storage sector. Despite these results, the stock fell 5.4% in regular trading to $519.17 and declined another 11.1% after hours to $461.42. The sell-off erased roughly 16% of the company's market value in two days.

The decline occurred despite the company posting a non-GAAP gross margin of 54.4% and an operating margin of 44.2%. According to Startup Fortune data, the primary driver was not a failure in execution but the valuation context. Shares had rallied more than 190% in 2026 prior to the report, driven by the AI storage trade. Investors had already priced in significant growth, leaving little room for error when the actual results, while strong, did not exceed the already elevated expectations.

Guidance Triggers Valuation Reset

Management issued fiscal first-quarter 2027 guidance for revenue between $4.0 billion and $4.2 billion, with adjusted EPS ranging from $3.85 to $4.15. These figures represented solid growth but failed to justify the nearly tripling of the stock price seen earlier in the year. The market interpreted the guidance as a plateau rather than an acceleration. This sentiment was echoed by rival Seagate, whose shares also wobbled following its own earnings beat days later, indicating a broader sector-wide reassessment of premium valuations.

By September 18, Western Digital shares closed at $441.36, a significant drop from the 52-week high of $799.87 recorded on June 18. The stock had lost approximately 45% of its value from its 2026 peak. This correction highlights the sensitivity of high-multiple tech stocks to guidance nuances, where even positive results can trigger selling if they do not exceed the aggressive benchmarks established by prior rallies.

Long-Term AI Storage Demand

The core business thesis remains intact, supported by long-term commitments from hyperscalers. CEO Irving Tan disclosed on the earnings call that Western Digital has a long-term agreement with a large customer running through calendar 2029. The company is also in discussions for further supply agreements extending into 2029, 2030, and 2031. These multi-year contracts indicate that large-scale AI data center builders are securing hard-drive supply well beyond the immediate quarter, validating the structural demand for high-capacity storage.

Recent market activity has shown investors becoming more selective in the AI infrastructure sector. On September 15, Western Digital shares fell 4% during the AI Infrastructure Summit, while Seagate dropped 5% and Micron remained stable. This divergence suggests that while demand for storage is robust, the market is differentiating between companies based on specific execution details and balance-sheet metrics. The company also announced the redemption of $109.5 million in convertible senior notes due 2028, a move that cleans up the balance sheet but did not offset the broader sentiment shift.

Sector Context And Peer Performance

Western Digital is not isolated in its volatility. SanDisk shares surged 726% in 2026, becoming the top-performing stock in the S&P 500, driven by an AI-fueled NAND memory shortage. However, the sector is entering a phase of scrutiny where individual earnings prints are weighed against already high expectations. The recent sell-off in Western Digital and Seagate marks a correction in the AI storage trade, where investors are re-evaluating which companies can sustain their growth trajectories at current price levels.