> Am I supposed to detect mobile devices (which is a massive pain) and serve them this separate HTML/JS/CSS? No. It's the responsibility of search engines and

> Am I supposed to detect mobile devices (which is a massive pain) and serve them this separate HTML/JS/CSS? No. It's the responsibility of search engines and apps to choose whether to send visitors to AMP pages. If Google crawls your site and finds AMP pages, it'll send mobile users to them from search.