Bun shipped 1M lines in nine days. The PR is the bottleneck now.

In June 2026, Bun, a software project, underwent a massive rewrite in Rust, resulting in a single pull request (PR) with 6,755 commits and over a million lines of code, highlighting the constraints of the traditional PR system. This rewrite, primarily authored by Claude over nine days, has underscored the shift in bottlenecks from code production to integration due to AI's capabilities in rapid code generation. The PR was too large for thorough human review, relying instead on automated tests and trust in the lead developer, which brought attention to the need for new approaches in handling such large-scale code changes. The article suggests that managing complex projects with a stack-based approach across multiple smaller, manageable PRs could facilitate better review, testing, and integration processes. This method would allow each part of the code to be independently reviewed, bisected, and reverted, maintaining human oversight while accommodating AI-accelerated production speeds.