Did Anthropic Just Lose Its Biggest Customer?

Cursor was Anthropic's biggest customer. Cursor co-founder Aman Sanger said so in January 2025: "We are without a doubt their largest customer." Now Cursor belongs to SpaceX, which also makes Grok. On October 12 Cursor launched new plans that include Grok but no Claude usage. Developers who sign up today can still use Claude in Cursor, but they pay for each Claude request on top of their plan. Anthropic has not lost Cursor as a customer. I think it has lost Cursor as its biggest customer, and that hurts a company that got nearly a quarter of its 2025 revenue from just two customers.

What changed in Cursor's plans

Until now a Cursor subscription came with Claude. The old $20 Pro plan included a pool of usage for outside models like Claude, according to Cursor's docs.

The new plans are part of what SpaceX calls The X Subscription, a bundle of Grok, Cursor and X Premium. xAI's announcement says each plan includes "at least twice as much coding usage with our models as the comparable Cursor plan." Its own models are Grok and Cursor's Composer. Outside models like Claude are "billed separately at API list prices via top-ups." The old plans are closed to new sign-ups. Current subscribers keep their included Claude usage until they switch.

Say you sign up for Cursor today and pay $30 a month for Premium. Your Grok requests come out of a weekly pool that is included in the price. Each Claude request is billed on top, for example Claude Opus 5.5 at $4 per million input tokens and $20 per million output tokens. On the $8 Plus plan you only get Grok models and cannot pick Claude at all.

I think a lot of Cursor users will stop using Claude because of this. When one model is included and the other costs extra from the first request, most people use the included one.

How Cursor ended up with Grok

In January 2025 Anthropic did not have enough GPUs for all of Cursor's traffic, as I wrote at the time. A year later, in January 2026, Anthropic cut off xAI developers who had used Claude through Cursor. xAI co-founder Tony Wu told his staff that this pushed xAI to build its own coding product and models.

In February SpaceX took over xAI, and on August 14 it completed its $60 billion purchase of Cursor. Within two weeks OpenAI said it will end Cursor's access to its models on November 12, because it "cannot be confident that SpaceX will use our technology within our terms of service."

Anthropic stayed. Its co-founder Tom Brown wrote: "Cursor has been a trusted partner of Anthropic since Sonnet 3.5. We'll continue to increase compute to support Claude models in Cursor and are excited for what comes next with them at SpaceX." Six weeks later Cursor moved Claude out of the included usage in its new plans.

Two customers made a quarter of Anthropic's revenue

Anthropic is getting ready for an IPO, and its draft prospectus shows how much it depends on a few customers. According to Reuters, Anthropic made almost $4.6 billion in revenue in 2025, and nearly a quarter of it came from two customers. The prospectus also warns that many of its largest clients are not locked into long-term contracts and could cut or stop spending.

The prospectus does not name the two customers. In August 2025, VentureBeat reported that Cursor and GitHub Copilot drove about $1.2 billion of Anthropic's revenue. I'm pretty sure Cursor is one of the two.

Cursor still pays Anthropic for the Claude requests its users make. Each user who moves to the included Grok usage lowers that bill.

Anthropic is growing fast enough that this won't sink it. Its revenue in the second quarter of 2026 was more than $11.5 billion, up from $787 million a year earlier, so Cursor is a much smaller part of Anthropic today than it was in 2025. But Anthropic is going public with a concentration warning in its prospectus, and Cursor now belongs to a competitor that pushes its own model. I think investors will notice.

The other big customer

The second big customer is most likely GitHub Copilot, which belongs to Microsoft. Since August, Copilot's automatic model selection can pick Microsoft's own coding model, MAI-Code-1.1-Flash, and that is how Copilot Free and Student users get it. Claude is still in Copilot, but Microsoft now has its own model to send requests to. In 2025 Cursor called itself Anthropic's largest customer, and by October 2026 it belongs to SpaceX and puts Grok first. Things change this fast now, so I would not be surprised if Anthropic loses more of its big customers the same way.

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