Bun contained approximately 535,000 lines of Zig code before the Rust rewrite.

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Location PART 3 - THE THIRD AXIS CHAPTER 15: DEPLOY NOW, PRAY LATER Zig & Godot

"Bun contained approximately 535,000 lines of Zig code before the Rust rewrite."

Sumner reports that the existing Bun codebase contained 535,496 lines of Zig excluding comments. This establishes the original implementation's scale and the engineering scope of the subsequent automated migration.

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Source title Rewriting Bun in Rust

Source authors Jarred Sumner

Source year 2026

Confidence high

Importance mid