According to Google, there are now more than 600 million AMP pages in 232 locals and 104 languages. That's not as many pages as i'd have expected by now, but, I guess much of it depends upon the development cycle.

Now when you search on your mobile device, you’ll see a label that indicates a page is AMP’d. This doesn’t change Search results but will show you which sites have pages that are ready to load lightning fast.Google Says SERPs are Officially AMP'd [search.googleblog.com]