Both the implementations of [jdk.internal.foreign.abi.Architecture] are singletons but do not have a privat constructor and is not final. This means a default constructor is generated:

  public jdk.internal.foreign.abi.x64.X86_64Architecture();
    Code:
       0: aload_0
       1: invokespecial #1 // Method java/lang/Object."<init>":()V
       4: return

Declaring the class final and introduce a private constructor would save 5 byte byte code and might potentially unlock other optimisations.