AES-NI is an extension of the instruction set of the CPU just like x64 extensions, or the older MMX, MMX2, SSE style extensions. They are opcodes that are hardw

AES-NI is an extension of the instruction set of the CPU just like x64 extensions, or the older MMX, MMX2, SSE style extensions. They are opcodes that are hardwired into the CPU itself. Software has to be compiled to take advantage of these additional instructions. Much like how you can compile software for say, i586 instead of i386, and get code that executes faster. so it all depends on how OpenSSH is compiled (and, to some extent, whether the OpenSSH source code has extract compiler flags/code sections)