2026-01-20
We built a browser with GPT-5.2 in Cursor. It ran uninterrupted for one week. It's 3M+ lines of code across thousands of files. The rendering engine is from-scratch in Rust with HTML parsing, CSS cascade, layout, text shaping, paint, and a custom JS VM. It *kind of* works! It still has issues and is of course very far from Webkit/Chromium parity, but we were astonished that simple websites render quickly and largely correctly.
Simon Willison's Weblog
Cursor recently experimented with using hundreds of AI agents to build a web browser; they ran for close to a week, writing 1M+ lines of code across 1,000 files
Scaling long-running autonomous coding. Wilson Lin at Cursor has been doing some experiments to see how far you can push a large fleet of “autonomous” coding agents:
@patrickc @cursor_ai Lots more to figure out, but perhaps a glimpse at the not-too-distant future. One concrete data point: a critical, isolated component of an upcoming launch was fully written by one of these “agent grind” sessions. It finished overnight and would've taken roughly an
Simon Willison's Weblog
Cursor recently experimented with using hundreds of AI agents to build a web browser; they ran for close to a week, writing 1M+ lines of code across 1,000 files
Scaling long-running autonomous coding. Wilson Lin at Cursor has been doing some experiments to see how far you can push a large fleet of “autonomous” coding agents:
Watch Cursor build a 3M+ line browser in a week [video]
Simon Willison's Weblog
Cursor recently experimented with using hundreds of AI agents to build a web browser; they ran for close to a week, writing 1M+ lines of code across 1,000 files
Scaling long-running autonomous coding. Wilson Lin at Cursor has been doing some experiments to see how far you can push a large fleet of “autonomous” coding agents: