Bun's Rust Rewrite: Six Weeks Later, Still No Release
Original: How is the Bun Rewrite in Rust going?
Why This Matters
AI-assisted large-scale open-source rewrites are being scrutinized for real-world delivery timelines and total cost transparency.
As of July 27, 2026, Bun's AI-assisted Rust rewrite — completed over 11 days at a cost of $165,000 in Anthropic API calls — has not produced a new release tag in 11 weeks, while open Claude-generated pull requests have nearly doubled to 2,475.
On July 8, 2026, Bun creator Jarred Sumner announced that Bun had been rewritten in Rust using Anthropic's AI tools between May 3–14, at a cost of $165,000 (~$15,000/day) in API calls. The rewrite was merged to main, but as of July 27, no new release tag has been published. The last release was bun-v1.3.14 on May 12, 2026 — an 11-week gap unprecedented in Bun's history since a six-week gap in late 2022. Developer Tom Lockwood investigated the repository and found that open pull requests from 'robobun' (a proxy for Claude Code-generated PRs) grew from 1,277 on July 9 to 2,475 by July 27. At an estimated ~40 minutes per merge pipeline run, clearing all open PRs would require approximately 86 continuous days of CI/CD. Lockwood also notes that the $165,000 figure appears to exclude Buildkite CI/CD costs, and that Anthropic employees are increasingly involved in direct commits. Bun was acquired by Anthropic prior to the rewrite, raising questions about whether the project serves as a marketing proof-of-concept for AI coding capabilities alongside Anthropic's valuation narrative.