Elon Musk's xAI cofounder Tony Wu sends email to employees, says: Anthropic has banned us, this is a..

Anthropic has cut off access to its Claude AI models for developers at xAI, Elon Musk's competing AI lab, according to an internal email sent this week by xAI cofounder Tony Wu to his team. "Hi team, I believe many of you have already discovered that Anthropic models are not responding on Cursor," Wu wrote on Wednesday, as first reported by tech journalist Kylie Robison.

"According to Cursor this is a new policy Anthropic is enforcing for all its major competitors."The block came after xAI staff had been using Claude models through Cursor, a popular AI-powered coding tool, to accelerate their own development work. Wu acknowledged the hit to productivity but framed it as motivation: "We will get a hit on productivity, but it rly pushes us to develop our own coding product / models."

xAI's Cursor usage violated competitive restrictions

The restriction appears rooted in Anthropic's commercial terms, which explicitly prohibit customers from using its services to "build a competing product or service, including to train competing AI models."

While Cursor itself is a legitimate development tool, xAI's specific use of Claude through the platform apparently triggered the enforcement action.This isn't the first time Anthropic has wielded its terms of service against rivals. Last August, the company revoked OpenAI's API access under similar circumstances, and in June 2025, it limited access for the coding environment Windsurf after reports emerged of a potential sale to OpenAI.

Anthropic's block on xAI aligns with wider enforcement against third-party tools

The xAI block comes as Anthropic simultaneously tightened technical safeguards against third-party tools spoofing its Claude Code client to access models at consumer subscription rates rather than metered API pricing. Thariq Shihipar, who works on Claude Code at Anthropic, confirmed the company had "tightened our safeguards against spoofing the Claude Code harness" after accounts were banned for triggering abuse filters.The timing is notable. Musk recently posted that a "major upgrade to Grok Code" is coming next month, promising it will "one-shot many complex coding tasks." Nikita Bier, head of X, responded to the Anthropic ban by suggesting: "Time to ban Anthropic from X."