Seagate ships HAMR Mozaic now, Western Digital waits to 2027

Seagate and Western Digital both closed fiscal 2026 with blockbuster quarters and nearly identical revenue guidance for fiscal Q1 2027, yet their technology paths have diverged sharply. Seagate is ramping HAMR-based Mozaic drives into hyperscale contracts today, with Mozaic 4 drives capable of up to 44 terabytes per drive already shipping for revenue to 75% of the leading global cloud customers by March. Western Digital, now a pure-play HDD company after the Sandisk separation, is stretching ePMR further before its own HAMR product ships in 2027.

The financials reflect this divergence. Seagate's gross margin expanded to 52.3% from 37.4% year over year, and free cash flow hit a record $3.1 billion for the year. Western Digital's exabyte shipments grew 22% year over year in Q4, but cost-per-terabyte fell only approximately 8% year over year. Seagate's HAMR economics appear to be pulling costs faster, though Western Digital trades at a lower forward P/E of 22 versus Seagate's 23.

The next test is HAMR qualification speed. Seagate's ability to push 70% of nearline exabytes onto HAMR by fiscal 2027 without yield issues is critical, while Western Digital's 44TB Hammer qualification with hyperscalers in early 2027 is key. Both names face risk if HAMR qualification slips or hyperscaler capex cools.