AMSI is present in all of the latest versions of Windows 10. But I'm pretty sure that Microsoft keeps playing with it, trying to get it right.
Things like AMSI are a gamble. When confronted with a script-based attack, AMSI might or might not block it. It depends upon how Microsoft made it.And I can tell you that AMSI is like Windows 10. You cannot know what Microsoft is doing because they won't say. And even if you did know, you cannot trust it. AMSI implementation is quite vague. I don't think that even the Microsoft developers know. Seems to me like they experiment a lot with AMSI.
If you are worried about malicious scripts, then the only proper way to handle them is to block script file types and their underlying interpreter\sponsor processes from launching.