---
title: "The Pulse: What can we learn from Bun’s rapid Rust rewrite with AI?"
url: https://daily.dev/posts/the-pulse-what-can-we-learn-from-bun-s-rapid-rust-rewrite-with-ai--dfcfl0hk9
source_url: https://blog.pragmaticengineer.com/the-pulse-what-can-we-learn-from-buns-rapid-rust-rewrite-with-ai
type: article
source: "The Pragmatic Engineer"
published: 2026-07-16T16:56:43.454Z
updated: 2026-07-19T04:04:52.258Z
tags: ["rust", "zig", "bun"]
reading_time: 12
upvotes: 1
comments: 0
language: en
---

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# The Pulse: What can we learn from Bun’s rapid Rust rewrite with AI?

**[The Pragmatic Engineer](https://daily.dev/sources/pragmaticengineer)** · 12 min read · 1 upvotes · 0 comments

## Summary

Bun's creator Jarred Sumner rewrote the entire Bun JavaScript runtime from Zig to Rust in just 11 days using Anthropic's Fable AI agent tool, at a cost of $165K in API tokens. The process involved 64 parallel Claude agents working across 1,448 files (535K lines of code), guided by a detailed 600-line porting guide created upfront. Key steps included prep work with Claude, parallel agent execution, adversarial review of each commit, and iterative compiler error fixing. The migration succeeded largely because Bun had a robust test suite. The takeaway: AI-assisted rewrites are now feasible for well-tested codebases, compressing what would have been a 1-2 year manual effort into under two weeks, though it requires a motivated engineer with deep codebase knowledge, a comprehensive test suite, and willingness to invest in token costs.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://blog.pragmaticengineer.com/the-pulse-what-can-we-learn-from-buns-rapid-rust-rewrite-with-ai>

---

Tags: [#rust](https://daily.dev/tags/rust), [#zig](https://daily.dev/tags/zig), [#bun](https://daily.dev/tags/bun)

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