> though it seems to be off by default since MSVC2022

This seems to be a typo in the docs, VS2022 is 17.x and still generates volatile metadata. VS2026 is 18.x.

Last time I tested it, the penalty in Prism for running x64 code without volatile metadata was ~25% on Snapdragon X.

ARM64EC code is essentially x64 code pre-translated to ARM64. It's built against the x64 emulation ABI conventions but runs directly as native ARM64 code. Translation thunking conventions allow for cross-calling between ARM64EC and emulated x64 code.

A lot of the OS libs are shipped in Windows 11 ARM as ARM64X, so they're hybrid ARM64EC+ARM64. x86 libs like MSVCRT.DLL do still seem to be compiled with volatile metadata. DUMPBIN /LOADCONFIG reveals if volatile metadata has been included.