Scaling long-running autonomous coding

Summary

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: This post describes what we've learned from running hundreds of concurrent agents on a single project, coordinating their work, and watching them write over a million lines of code and trillions of tokens. They ended up running planners and sub-planners to create tasks, then having workers execute on those tasks - similar to how Claude Code uses sub-agents. Each cycle ended with a judge agent deciding if the project was completed or not. In my predictions for 2026 the other day I said that by 2029: I think somebody will have built a full web browser mostly using AI assistance, and it won’t even be surprising. Rolling a new web browser is one of the most complicated software projects I can imagine[...] the cheat code is the conformance suites. If there are existing tests that it’ll get so much easier. I may have been off by three years, because Cursor chose "building a web browser from scratch" as their test case for their agent swarm approach: To test this system, we pointed it at an ambitious goal: building a web browser from scratch. The agents ran for close to a week, writing over 1 million lines of code across 1,000 files. You can explore the source code on GitHub. But how well did they do? Their initial announcement a couple of days ago was met with unsurprising skepticism, especially when it became apparent that their GitHub Actions CI was failing and there were no build instructions in the repo. It looks like they addressed that within the past 24 hours. The latest README includes build instructions which I followed on macOS like this: cd /tmp git clone https://github.com/wilsonzlin/fastrender cd fastrender git submodule update --init vendor/ecma-rs cargo run --release --features browser_ui --bin browser This got me a working browser window! Here are screenshots I took of google.com and my own we...