Gary Illyes may have been misunderstood or may have misspoke at the Brighton SEO conference a few weeks ago when people said he said that when the mobile first index rolls out, Google will index the AMP URL when there is no mobile version of the site but there is an AMP and desktop version. Of course, we all know the chances of there being AMP and no mobile URL is rare but in that case, Google will not index the AMP version, they will index the mobile version.
John Mueller confirmed this in a hangout yesterday at the 32:31 mark saying that Google will index the desktop version if the AMP version is not set as your mobile version using the rel alternate set up for mobile. So if you have desktop, AMP and no mobile - Google by default will index your desktop version of your site.
Google said this before about a year ago but there was some confusion around this the other week out of that conference.
Here is the video embed at the start time of when John said this:
Question: You said don’t worry if you don’t have a mobile site, but you have an AMP version, will Google index the AMP version or the desktop version?
Answer: We will index the desktop version. Unless you are setting it up as AMP as both rel AMP HTML and rel alternate for the mobile set up. You can theoretically set it up with the AMP version as the separate mobile URL of the desktop page. But if you don’t set that up and you just have the rel AMP HTML, we will take the normal desktop page because that’s the canonical page essentially.
Question: And that is how it will happen with the mobile first index?
Answer: Yes.
Here are some of the confusing tweets around this:
#amp pages will be indexed first for the mobile index before responsive pages #SEO #BrightonSEO #garyillyes
— Innovation Visual (@InnovationVis) September 15, 2017
For mobile first, Google will crawl AMP version of page. Keep dat in mind! #brightonSEO pic.twitter.com/LBjfwbVwwV
— Noisy Little Monkey (@noisymonkey) September 15, 2017
Here is Gary apologizing:
I may have gotten this wrong. I think I answered "if the only version" not "if the only *mobile* version" -_- I'll check with the team tho
— Gary "鯨理" Illyes (@methode) September 19, 2017
Forum discussion at Twitter.