OpenAI cut off Cursor. The 5% number is the whole story

Late last week, @OpenAI posted a breakup note: "We're ending our partnership with Cursor following its acquisition by SpaceX." Under OpenAI's proposal, Cursor, the AI code editor, loses direct access to OpenAI models on November 12, about three months after SpaceX closed its $60 billion purchase of the company on August 14.

The stated reason is trust. OpenAI says it can't be confident SpaceX will use its technology within its terms of service, and it points to history: Twitter cutting off OpenAI's data access after Musk bought it in 2022, and Musk admitting under oath this year that xAI had violated OpenAI's terms. You can decide for yourself how much of this is principle and how much is a long-running feud finding a new venue. Probably both.

What made the weekend interesting was the response. Cursor CEO Michael Truell (@mntruell) replied the next day, and one number did most of the work: "OpenAI models serve about 5% of Cursor user traffic." He said the two teams are talking, and he noted that Cursor was one of OpenAI's earliest customers and had trusted its platform to be neutral infrastructure.

Within a day, Anthropic co-founder Tom Brown (@NotTomBrown) showed up with an open hand: "We'll continue to increase compute to support Claude models in Cursor." He called Cursor a trusted partner since the Sonnet 3.5 days and said Anthropic is looking forward to working with them under SpaceX.

The 90-day notice

As far as I can tell, this is the first time a frontier lab has pulled its models from a major paying customer because of who acquired it, rather than anything the customer did with the product. That precedent matters more than the feud behind it. If your product or your operations run on a frontier model, your access now depends partly on relationships between companies you don't control, and it can end with a blog post and a 90-day clock.

"Neutral infrastructure" is the phrase in Truell's reply worth sitting with. He used it the way you'd talk about a power company. Last week showed that model access isn't that. It's a business relationship, and business relationships have moods.

Why Cursor gets to shrug

Because of the 5%. Cursor runs models from several labs, and its users had already drifted toward other providers, which is how OpenAI's share of traffic got that low in the first place. Supporting all those models looked like a cost for years: more integrations to maintain, more contracts, more testing every time a lab shipped something new. Last week that cost converted into leverage. Losing OpenAI is a haircut, not a shutdown, and the calm in Truell's post comes straight from that number.

Notice the other side of the same mechanism. The moment one supplier walked, another publicly offered extra compute within a day. When your customers can switch, you keep competing for them even after you've won them. Cursor built itself into the kind of customer suppliers fight over, and it did that with an architecture decision, not a negotiation.

Know your own five percent

If you've wired AI into your business, into quoting, intake, or follow-up, this story hands you one concrete question: if the model behind your workflow got a 90-day notice tomorrow, what percent of your operation stops? Cursor's answer was 5. For a lot of small businesses the honest answer is 100, because the whole process lives inside a single vendor's tool, with the prompts and data tangled into the logic in one place.

Avoiding AI is the wrong lesson to take from that. The right one is Cursor's: keep your data and your process logic on your side, and treat the model as a part you can swap. That's how we build automations at New Face Design, and if you don't know your number, our free process audit will find it, step by step: which parts of your operation depend on which vendor, and what it would take to make any of them replaceable.

Cursor has until November 12. You get to pick your own deadline.