Many of the capabilities described in the article are just hardware features which don't need any control from application developers, but their effectiveness can be improved if the developers are aware of them (e.g. caches, TLBs). Others properties are exploited automatically by compilers (e.g. instruction scheduling for improving throughput in a superscalar processor)

Instruction set extensions (which I believe might be what you were thinking of) are used via intrinsics and assembly programming by pretty much any performance-oriented code. For example look at the dozens of architecture-specific implementations of glibc functions: x86-64[0], arm[1].

[0] https://sourceware.org/git/?p=glibc.git;a=tree;f=sysdeps/x86... [1] https://sourceware.org/git/?p=glibc.git;a=tree;f=sysdeps/arm...