In Rust this is only guaranteed to be true of "tier 1" targets. Rust also supports many "tier 2" and lower targets where the guarantee is only that the standard library will build (not that it actually works) and even then on some platforms only the core is supported.

That’s not true; the Rust standard library contains things that are OS/architecture specific.

(Anyway, in rust cross target compatibility is usually not a worry if you’re not using unsafe, a dependency that uses C libraries)

All standard libraries contain OS specific code for their implementation.

yeah that was the point - less guarantees that something works forever means less maintenance. in the current world the balance is with leaner stdlibs because discovery and acquisition of external libraries is so simple.