Claude Code Has Run on Rust-Bun for a Month and Nobody Noticed
Simon Willison dug into the Claude Code binary and confirmed something quietly remarkable: since v2.1.181, released June 17, Claude Code has been shipping the Rust port of Bun. The evidence is right in the binary β 563 Rust source filenames, Bun v1.4.0 preview embedded. Startup got 10% faster on Linux. Otherwise, nothing happened. Which is exactly the point.
The backstory makes it spicy. Bun's team ported 535K lines of Zig to Rust in 11 days using coordinated parallel Claude agents, at roughly $165,000 in API pricing. Zig's creator called the result unreviewed slop, and the argument burned across the ecosystem for a week. Meanwhile, the port went into production inside the world's most heavily used coding agent, running on millions of machines, for a month, in silence.
Willison's verdict is two words: boring is good. It is also the strongest counter-argument available in the slop debate. You can argue about review processes all day; a month of production silence across millions of devices is data. The largest AI-driven rewrite ever attempted is no longer a demo or a controversy β it is infrastructure you are already running.
Post: https://simonwillison.net/2026/Jul/19/claude-code-in-bun-in-rust/
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The backstory makes it spicy. Bun's team ported 535K lines of Zig to Rust in 11 days using coordinated parallel Claude agents, at roughly $165,000 in API pricing. Zig's creator called the result unreviewed slop, and the argument burned across the ecosystem for a week. Meanwhile, the port went into production inside the world's most heavily used coding agent, running on millions of machines, for a month, in silence.
Willison's verdict is two words: boring is good. It is also the strongest counter-argument available in the slop debate. You can argue about review processes all day; a month of production silence across millions of devices is data. The largest AI-driven rewrite ever attempted is no longer a demo or a controversy β it is infrastructure you are already running.
Post: https://simonwillison.net/2026/Jul/19/claude-code-in-bun-in-rust/
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