Cursor: AI Writes 3M Lines in 168 Hours to Build a Browser
Cursor's 168-hour AI swarm wrote 3M lines to build a browser, proving agentic coding scales and open-sourcing the repo
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AI Writing Code: This Time It’s Gone Big
The founder of Cursor announced the results of a wild experiment: hundreds of AI agents ran continuously for an entire week, starting from scratch, and forcibly built a functional web browser.
Code-named FastRender, the project produced over 3 million lines of code, with a core rendering engine written in Rust from the ground up, even including a custom JavaScript virtual machine.
Truell described the browser as “barely usable,” far from the mature Chrome engine, but already capable of correctly rendering Google’s homepage.
The entire project source code has been made public on GitHub.
The Brain Behind It: GPT-5.2-Codex
This experiment succeeded thanks to GPT-5.2-Codex, released by OpenAI in December 2025.
