⚠ Online Is Where Costco Has No Structural AdvantageHigh threat

Every source of Costco's cost advantage is physical, and none of them travel to a website.

The pallet display that removes labour becomes a picker walking an aisle. The 4,000-item assortment that concentrates buying power becomes 9,000 to 10,000 items online¹ and rising, because a site with no shelf constraint loses the search to a site with more choice. The thirteen inventory turns achieved by selling in case quantities become individual units shipped in individual boxes. The controlled entrance that keeps shrink below typical retail becomes a returns process. And the membership gate, which is the whole business model, becomes a login that a competitor does not require at all.

What is left online is delivery speed, price, and assortment — the three dimensions on which Amazon and Walmart have spent thirty years and hundreds of billions of dollars building infrastructure Costco has not built. Costco's own risk factors concede the shape of it: competitors have "greater financial resources and technology capabilities, including the faster adoption of artificial intelligence, better access to merchandise, and greater market penetration"², and the evolution of online retailing "has improved the ability of customers to comparison shop, which has enhanced competition."

None of this means the digital business is a mistake; a membership that only works when you drive somewhere is a membership with a demographic clock on it. It means the growth is happening on the one battlefield where Costco's advantages do not apply.

What separates the two readings is the relationship between digitally-enabled growth and frequency. Rising digital with rising frequency means the channel is additive. Rising digital with frequency at 2 points, which is where the third quarter of fiscal 2026 sat³, is the pattern that should worry a shareholder.