How is the Bun rewrite in Rust going?
Points and comments are a snapshot, not live.
Analysis questions the costs and completeness claims of Bun's Rust rewrite by Anthropic.
The author analyzes Bun's claimed 11-day Rust rewrite costing $165k in Anthropic API calls. As of July 27, 2026, six weeks post-merge, no release tag exists; the last release was May 12. Open PRs from robobun grew from 1,277 to 2,475. Anthropic employees actively contribute to Rust code. The author estimates ongoing daily costs may approach $10k, totaling near $800k, and notes Anthropic's C compiler and Cursor's FastRender browser have seen no commits for months.
What commenters are saying
Top commenters express skepticism common in tech: the rewrite works fine for most users but the true costs and idiomatic quality remain questionable. Several argue an LLM rewrite produces unidiomatic Rust with excessive `unsafe`, losing memory safety benefits; others counter that deterministic linting and tools like `miri` can target `unsafe` usage effectively. A key tension emerges: the $165k claim omits human engineer guidance and ongoing CI/CD costs. Some suggest the rewrite may be complete in the sense of no Zig remaining, with current activity paying down tech debt.