How is the Bun Rewrite in Rust going?

I think it’s important to be very Canny when someone makes a claim that supports a company’s large valuation.

The Bun rewrite seems well positioned as proof-positive that AI and specifically Anthropic’s AI can do the work of open-source maintainers, for some money, but faster.

On the 8th of July 2026 Jarred Summner of Bun fame posted about “Rewriting Bun in Rust”. At the time, I felt pretty Canny, having already read about Anthropic’s C compiler and Cursor’s FastRender web browser. It seems like there is a lot of valuation money riding on the coding capabilities of AI, and a lot of marketing about those capabilities.

It’s not a huge stretch to link the acquisition of Bun by Anthropic with the choice to rewrite Bun with an Anthropic tool. In his article Jarred claims that over 11 days (between 3rd and 14th May 2026) and at a cost of $165,000 for Anthropic API calls the rewrite was done and then merged to main. This represents a cost of $15,000 dollars a day, a cost well outside the means of many open source maintainers. This number doesn’t seem to include the leviathan whirring of the CI/CD in the org’s Buildkite cluster, which appears to have been constantly whirring ever since the “rewrite” was “completed”.

Why do I put those two words in scare quotes?

Well, on the 9th of July a peer of mine in a group chat said something unsurprising given our current environment - breathlessly proclaiming that the era of AI had emerged, and its herald was the “Rewriting Bun in Rust” blog post. So, I decided to look into this. Since the 9th I’ve been having a closer look at the claims and the code, and today I cloned the Bun repo:

Receiving objects: 100% (1200304/1200304), 1.23 GiB | 11.97 MiB/s, done.

As of today, the 27th of July 2026, a six week period after the rewrite was merged to main, there’s still no release tag. It’s now been 11 weeks since the last Bun release tag:

2026-05-12 15:12:49 -0700 (tag: bun-v1.3.14)