[niftich]

Google Search, when used from a mobile user-agent, such as a mobile browser or some mobile-resident Google Search integration like the Google Now Launcher Search Bar, will show some results' AMP-equivalents, and uses AMP-availability as a ranking signal.

When such an AMP search result is opened from the aforementioned Google Search source, it will open in a Google Search-wrapped frame reader, such that the outside is Google Search -- although this is not visually obvious to the user -- while the inside the AMP article. The browser-level URL for this endpoint begins with 'google.com/amp/'. While it's now possible to get the article's original link from this viewer, this was not present at launch, and it was a frequent source of criticism.

This is a brief restatement of a more in-depth description I gave in a different thread [1].

[1] https://news.ycombinator.com/item?id=14385122