Bun

Overview

Bun is a fast JavaScript/TypeScript runtime and toolkit, acquired by anthropic in December 2025. Originally written in Zig; rewritten to Rust in July 2026 using Claude agent fleets.

Recent Developments

• 2026-08-04: shai-hulud-worm dropper downloads Bun v1.3.13 as second-stage runtime (user-agent IOC Bun/1.3.13 per wiz) (2026-08-04-wiz-keyv-cacheable-npm-attack)
• 2026-07: Zig→Rust rewrite in 11 days via ~50 Claude Code workflows; ~1M LOC; ~$165k API cost; Claude Fable 5 (pre-release) (2026-07-15-bun-rust-rewrite-official)
• Zig creator Andrew Kelley criticized approach as “unreviewed slop” (2026-07-14-zig-creator-bun-claude-rust-rewrite-criticism)

Related

• anthropic
• zig
• claude-code
• ai-code-rewrite
• andrew-kelley
• javascript

Sources

• 2026-07-15-bun-rust-rewrite-official