The long, weird symbiosis between AI coding tool Cursor and its primary model provider Anthropic has finally been laid bare. Business Insider reports that internal employees describe the relationship as deeply strange — Cursor relied on Anthropic’s API for its core coding features, while Anthropic collected an estimated 40 to 50 percent of its early revenue from Cursor users. But even as they benefited each other, Anthropic was quietly building a competitor.
Before launching its terminal coding tool Claude Code, Anthropic execs privately assured Cursor’s management that it was just an academic experiment with no commercial ambitions. Then Claude Code took off. By February 2026, its annualized revenue hit $2.5 billion — leapfrogging Cursor’s $2 billion. Cursor lost its technical exclusivity, and developers began jumping ship, posting online that they had canceled their subscriptions to switch to Claude Code.
The deeper fear was a model cut-off. When Windsurf, another AI coding tool, was in acquisition talks with OpenAI, Anthropic suddenly cut off Windsurf’s model supply. That was a wake-up call for Cursor. On January 5, founder Michael Truell held an emergency all-hands meeting and decided to go all-in on building its own model. Cursor then developed the Composer series based on Moonshot AI’s open-source model. By this May, Composer 2.5 was more than 85 percent self-developed, delivering low price and high concurrency while reducing dependence on big AI labs’ APIs.