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Anthropic bought Bun, then had its coding agents rewrite the entire JavaScript runtime from Zig to Rust — roughly 535K lines, 64 parallel agents, done in days, “near 100%” AI-generated. Official reason: Zig’s memory bugs, about four fixes a week, forced the switch.

Zig creator Andrew Kelley isn’t buying it. The bugs came from bad engineering decisions — chiefly letting AI agents write and review everything — not from the language. TigerBeetle runs mission-critical Zig with static allocation and a strict style guide, and doesn’t have this problem. The fix was discipline, not Rust.

Why HN gave this 1,085 points

Ray Myers, former chief architect at a coding-agent startup, went further: the rewrite is marketing. Anthropic’s write-up skips the costs — build times got worse, and Bun had literally forked the Zig compiler for speed — and reads like post-hoc justification for an “AI is enough” story. 545 comments, most siding with Kelley.

Why it matters

This is the first large-scale public challenge to the “AI rewrote our codebase” narrative. Every AI vendor wants that headline; nobody publishes the tradeoffs. Kelley just made the omissions the story.

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