Cursor, an AI-powered software development environment, has quietly added a new large-language-model option called “Sonic” for all users. The model—which presents itself as xAI’s Grok—went live on 20 Aug. and is being offered free of charge inside the editor. Early user tests posted online show Sonic producing as many as 3,100 lines of HTML code in a single generation and generally outperforming Cursor’s existing models on coding tasks, according to the first public screenshots and videos. Cursor has not issued a formal announcement or documentation, and xAI has not commented on whether Sonic is an official repackaging of Grok.