Thanks for the hint. According to public sources, Bun's runtime infrastructure and bindings are written in Zig, but it uses Apple's JavaScriptCore engine written in C++ (i.e. Zig is essentially used in a thin wrapper layer around a large C++ engine). Bun itself apparently struggles with stability and production readiness. Oven (Bun's company) has around 2-10 employees according to LinkedIn.

Been using bun from years, it's as stable as alternatives from a long time.