It's not hidden from the public APIs. It's exposed through Accelerate.framework, etc. The instructions themselves aren't stable so there's no guarantee they'd e

It's not hidden from the public APIs. It's exposed through Accelerate.framework, etc. The instructions themselves aren't stable so there's no guarantee they'd exist in other generations - as others have said these instructions predate ARM actually adding the standardized scalable vector extension, presumably Apple could switch to the standard ISA in future, but if the AMX instructions were exposed directly to developers they'd have to continue to support them in future and thus continue to burn silicon space for them.