Anthropic’s growth has been staggering, but its IPO prospectus shows how much of that growth rested on a very small number of buyers.
According to Anthropic’s IPO prospectus, seen by Reuters, nearly a quarter of Anthropic’s 2025 revenue came from just two customers. The company also warned investors that many of its largest clients aren’t locked into long-term contracts and could cut or stop spending.
The prospectus, as reported so far, doesn’t name the two customers. One report on the filing says each accounted for about 12% of 2025 revenue. On Anthropic’s roughly $4.6 billion in revenue for the year, that works out to something like $1.1 billion between them.
Who Are Anthropic’s Two Biggest Customers?
Anthropic hasn’t confirmed the identities, so this is informed speculation. But there’s a strong candidate pair.
Last year, VentureBeat reported that AI coding tools Cursor and GitHub Copilot were driving roughly $1.2 billion of the $5 billion run-rate Anthropic had reached at the time, or close to a quarter of the total. Both products let developers pick Claude models, and Anthropic’s models have been a staple of coding tools for a while. Cursor’s documentation still lists the latest Claude models, including Opus 5.5 and Sonnet 5.5, as options.
The numbers line up neatly with what the prospectus now describes, although a run-rate figure from mid-2025 and full-year recognized revenue aren’t the same thing, so this is a consistency check rather than confirmation.
There is another possibility worth mentioning. Anthropic sells through Amazon, Google and Microsoft’s cloud platforms, and it has been accused by rivals of booking that cloud partner revenue on a gross basis, which means those channels could show up as large “customers” on paper. OpenAI has argued that this accounting choice inflates Anthropic’s run-rate, though both approaches are permitted under US accounting rules. The reported description of the two customers as “direct” ones, though, makes the coding tools the more likely explanation.
Is This Level Of Customer Concentration Unusual?
It depends on what kind of company you compare Anthropic to.
For a typical software-as-a-service business, having two customers make up a quarter of revenue would be a red flag. Public companies are generally required to disclose any customer above 10% of revenue, and most SaaS firms sell to thousands of buyers so that no single account matters much.
But Anthropic looks less like a conventional software company and more like a supplier of a critical input, and in that world concentration is common. CoreWeave’s IPO filing showed Microsoft accounting for the majority of its 2024 revenue, and chipmakers routinely disclose a handful of customers with double-digit shares.
It also isn’t just a Cursor-and-Copilot story. Data from Ramp shows that at both Anthropic and OpenAI, the top 1% of customers generate roughly 80% of enterprise revenue, a concentration Ramp’s lead economist said exceeds any other software category the firm tracks. Frontier AI, in other words, is an unusually top-heavy business across the board.
The Case That Concentration Is Fading
There are reasons to think the 2025 picture overstates today’s dependence. Anthropic’s annualized revenue run-rate has since climbed past $47 billion, far beyond the $9 billion or so it stood at when 2025 ended, and much of the recent growth has come from its own products such as Claude Code, along with a rapidly widening base of large enterprise customers. The number of customers spending over $1 million a year has risen sharply.
Anthropic has also shown it’s willing to use its leverage over distribution. It has previously cut off Windsurf after reports that OpenAI would acquire it, and it cut off xAI’s access to its models on Cursor. Those moves show Anthropic isn’t a passive supplier, but they also show how much of its business flows through third-party products it doesn’t control.
What Investors Will Watch
The prospectus figure is a snapshot of 2025, not of today. What public-market investors will want to know is how the top-customer share has moved since, whether the biggest accounts have signed longer-term commitments, and how much of Anthropic’s growth now comes from products it owns directly. Until those answers are clear, the two-customer disclosure will remain one of the more closely watched risk factors in the filing.