Western Digital in the AI stack

The business and what the filings show

Western Digital now makes only hard-disk drives, after separating its flash business into Sandisk. That sounds like the old part of storage, but hard drives still hold most of the world’s data at the lowest cost per terabyte, and the cloud builders buy them in huge volumes. Over its latest four quarters Western Digital reported $14.5B of revenue, +43%, at a 53% gross margin and a 39% operating margin, with free cash flow of $4.3B.

Its customer base is narrow. The Cloud end market accounted for 89% of its fiscal 2026 revenue, its top ten customers for 73%, and three customers each passed 10%, at 16%, 15% and 13%. Those customers are the same hyperscalers whose capital spending drives the rest of this map, so Western Digital’s results are in effect a reading of how much bulk storage they add.

The investment case rests on discipline more than technology. Only three companies still make hard drives, Western Digital and Seagate lead at the highest capacities, and both have kept capacity tight as demand rose. Margins have climbed as a result; the question is whether that discipline holds when demand stops rising.

How AI shows up in the numbers

AI shows up at Western Digital as demand for the high-capacity drives that store training data, model checkpoints and the content AI services generate. Flash is faster, but hard drives remain far cheaper per terabyte, so the data that isn’t being used at that moment usually lives on them. The company’s 10-K describes data storage as the foundation of an AI-driven data economy; the numbers to test that against are Cloud revenue and exabytes shipped.

For scale, Western Digital’s revenue over the latest four quarters equals 3% of the $566B the five largest buyers spent on capital projects over their latest four quarters. Their capex rose +81% on the year before, while Western Digital’s revenue grew +43%: slower than the spending, so it is capturing a smaller share of each new capex dollar, or more of its business sits outside the build-out.

How it talks about AI

Western Digital is not yet in the set of companies whose earnings releases we read sentence by sentence, so this section quotes its annual report on Form 10-K instead. Statements in a 10-K carry more weight than a press release or an earnings call: they are part of a filing the company signs and can be held to, and the risk factors in particular say what management believes could go wrong. The sentences below are quoted from its latest 10-K.

Read them for two things: how directly the company ties its growth to AI, and how much it is willing to quantify. A company that names AI as its main growth driver is making a claim its revenue mix can be checked against in the next filing; one that says AI’s effect is hard to measure is telling you its numbers won’t isolate it.

The figure to set these statements against is Western Digital’s own growth: revenue +43% over its latest four quarters at a 53% gross margin. If AI is driving the business as described, the next filings should show it in the mix of revenue by product or customer, and in margins that hold up as volumes grow.

• On its strategy: “At Western Digital, we believe that data storage provides the strategic foundation for the AI-driven data economy.” 10-K, August 14, 2026
• On hard drives: “While this growth has led to the creation of several form factors for data storage and an increasing use of a tiered architecture approach, HDDs occupy a unique place in the market by providing an economical means to create, store and utilize an increasing amount of data in the age of AI.” 10-K, August 14, 2026

The trend in the numbers

Since the start of 2023, Western Digital’s largest quarter by revenue was Q3 2026 at $4.4B, and its highest gross margin was 58% in Q3 2026. The latest quarter set the revenue record for the period.

Quarter by quarter, Western Digital’s revenue grew +25% in Q4 2025, +45% in Q1 2026, +44% in Q2 2026, +55% in Q3 2026 on the same quarter a year earlier. Growth has been accelerating.

Gross margin in the latest quarter was 58%, against 44% a year earlier, so it is keeping more of each dollar as it grows. Operating margin moved from 28% to 47% over the same span. Over the latest four quarters it turned 34% of its revenue into operating cash flow and spent 4% of revenue on capital projects, against 4% a year earlier.

Where it sits in the stack

Western Digital sits in the memory and storage layer of the AI stack. It is paid by the servers and chips layers; its own spending flows to foundry & tools.

Among the 5 companies in this layer on our map, it ranks number 3 by revenue and number 4 of 5 by revenue growth. Its gross margin of 53% compares with 75% for the layer as a whole, so it keeps less of each dollar than the layer average. The full layer analysis is on the memory page.

Latest four quarters for 10-Q filers; latest fiscal year for 20-F filers. Companies under $100 million of revenue are left out.

Against the 5 US-listed companies in its layer, Western Digital grew +43% over the latest year versus +180% for the layer combined, and converted 30% of revenue into free cash flow versus 43% for the layer. It is growing more slowly than its layer, so its share of the layer’s revenue is shrinking.

What has to go right, and what could go wrong

What has to go right. Cloud customers have to keep adding bulk storage as AI generates and retains more data, and the industry has to keep adding capacity cautiously enough to hold prices.

What could go wrong. Three customers account for over 40% of revenue, so a pause by any of them would show immediately. Faster price declines in flash could also move some workloads off hard drives.

These describe the conditions the business depends on, as the filings show them. They are not a view on the stock.

Through the lens of Investing in AI

Rob May’s book offers six mental models for telling AI moats from traps. The one most useful for Western Digital’s layer is “Be careful evaluating AI COGS”: AI margins can improve dramatically as human labor comes out, or deteriorate as inference bites. Some companies reach software-like margins; others stay closer to services. Underwrite the trajectory, not today's margin.

The question it asks of any company is: Why will gross margin be higher in three years, and what could stop it? Applied to Western Digital, the filings on this page are the place to start: the margin trend shows whether it holds scarce value or passes it through, the customer and financing disclosures show who it depends on, and the commitments show what it has promised before the revenue arrives.

Customers and concentration

US companies must disclose any customer that accounts for 10% or more of revenue, and foreign filers usually describe their largest customers. Concentration matters because a company’s growth is only as durable as the handful of buyers behind it, and in the AI stack those buyers are often the same few companies.

• “For 2026, three customers accounted for 16%, 15%, and 13%, respectively, of our net revenue.” 10-K, August 14, 2026
• “For the year ended July 3, 2026, the Cloud end market accounted for 89% of our net revenue and our top 10 customers accounted for 73% of our net revenue, with three customers each accounting for 10% or more of our net revenue.” 10-K, August 14, 2026

Commitments and backlog

• Backlog. Western Digital doesn’t report a comparable total of remaining performance obligations in its XBRL data.
• Purchase commitments. $304M of unconditional purchase obligations as of October 2, 2026 (10-Q): what it has contracted to buy from its own suppliers.

What to watch

Western Digital’s next quarterly report will cover the quarter ending around January 1, 2027. Large companies must file a 10-Q within 40 days of a quarter’s end and a 10-K within 60 days of the fiscal year’s end, so the new figures should arrive by about March 2, 2027 at the latest. This page, the layer pages and the next quarterly report all update from that filing.

• Cloud revenue and the share of revenue from the top three customers, given how concentrated its business is.
• Gross margin, which shows whether the two hard-drive makers are keeping supply disciplined.
• Capex at the cloud buyers: storage purchases follow their data-center build-outs.
• Its place in the next quarterly AI Stack Report, which updates every company on the map from the new filings.

Figures from Western Digital’s SEC filings, latest period ended October 2, 2026. Other companies: all company pages.