Cursor builds browser with AI agents

Cursor published a new blog revealing it ran hundreds of AI coding agents autonomously for weeks on end with one experiment producing a 3M+ line web browser built entirely from the ground up using GPT 5.2.

Cursor organized agents into planners, workers, and judges (similar to the viral Ralph Wiggum technique), allowing hundreds to run and collaborate together.

The browser was built in under a week by the agents from scratch, with the final output actually loading simple websites correctly.

Other experiments included a Windows 7 emulator, an Excel clone, and an internal migration of Cursor's codebase, each spanning a million+ lines of code.

The team also noted that GPT-5.2 handled long autonomous runs significantly better than Claude Opus 4.5, which tended to take shortcuts.