Zig's Creator on Bun's Rust Rewrite: Good Riddance

Andrew Kelley, creator of the Zig programming language, offers a scorching post-mortem on his years-long relationship with Bun and its founder Jarred Sumner. Bun, the JavaScript toolchain originally built in Zig, recently announced a rewrite in Rust following Bun-maker Oven’s acquisition by Anthropic. Kelley recounts how Sumner started as an energetic newcomer who generously credited Zig and donated $60,000 a year to the Zig Software Foundation, but says the relationship soured once Bun took venture capital and Sumner shifted from open-source contributor to startup manager with a reputation for grueling expectations and poor communication.

Kelley’s central grievance is engineering quality. He describes Bun’s codebase as a pile of hacks, abused assertions, and accumulated technical debt that made it an embarrassing poster child for Zig at a moment when the language faces relentless scrutiny over memory safety. He argues Bun’s problems stemmed not from Zig’s lack of features but from a refusal to invest engineering time in finding and fixing bugs — pointing to TigerBeetle as a counterexample of a Zig project that does the work. The Anthropic acquisition, he says, quietly ended the donations and the standing meetings, and the Rust rewrite came as a relief that puts distance between Zig and both Bun’s reputation and the flood of AI-driven ‘slop’ contributions.

The piece also rebuts specific claims in Bun’s rewrite announcement, which Kelley frames as polished corporate marketing. He disputes the idea that a good test suite alone can catch bugs in a million lines of unreviewed code, notes that the touted performance gains come from link-time optimization that Zig has long supported, and flatly calls Bun’s claim to have been fuzzing its Zig code a fabrication, saying the Bun team told him otherwise directly. Beneath the personal jabs, the essay is a pointed argument that language choice matters far less to software quality than the discipline and resources a team is willing to spend.