Just happened to me last week (I got the notification) and Googlebot hammered my site like yours the week before that so probably within 4 to 5 days you will get the notice after Google bot goes back to normal.

To early to say with traffic especially since we got hit 2 weeks ago by the Google algorithm.

Got hammered on two sites, one with 250k pages and other with 38k pages. Googlebot traffic is back to normal now, but only got the mobile index notice on the smaller site.

I haven't seen any difference. I had one site included months ago and one just last week.

Just got included on the 19th...on the 19th search traffic dropped 20% and has been lower since. But it's really too early to tell. Placement in SEMrush has unchanged so far

I'm with NickMNS. No obvious effects for better or for worse. We've seen steady increases in mobile at the expense of desktop, but that was happening long before Google introduced its "mobile first" index.

Thanks all. No message received yet, but the crawl surge has continued - think I need to bill Google for the bandwidth... they must have taken every page a couple of times by now... and it's a big site.

Hello wavingdave and welcome to WebmasterWorld [webmasterworld.com]

3 sites reindexed within a couple months and I saw little difference since the sites were responsive for a couple years and the content is the same for all devices, just the presentation changes.

That's what Google suggeseted to do so that's how we did it.

My approval came in on 2018 Sept 20 for a couple of sites. Yay from Google, but what does it actually mean for search rank? I've been responsive for years.

[edited by: TorontoBoy at 8:40 pm (utc) on Sep 23, 2018]

what does it actually mean for search rank?

It means your site is now ranked on the merits of the mobile version. If there is no current mobile version, your desktop version will continue to be ranked for this new index (at least for a while.)

Related discussion: Mobile-First Index [webmasterworld.com]

I currently have two sites notified - I did have three before switching them all over to https (which means a different site in GSC and, I suppose, a reset in the Mobile-First classification).

The sites are all responsive, not with separate mobile version or AMP, and not blazingly fast (although they do mostly follow 'good practices').

Site #1 - average GSC mobile position is top 10, average desktop position is outside top 20, average CTR is better with mobile but not stunning on either
Site #2 - average GSC mobile position is just outside top 5, average desktop position is within top 20, average CTR (<1%) is junk on both

Re the most recent change: site #2 was not one of the original three and is not a particularly obvious target to switch (it is relatively new and I have other more popular sites with more visitors and much higher ctr).
About 6 weeks before the notification there was a substantial jump in impressions (double) both on desktop and mobile and a related immediate decline in CTR (remember this is CTR from the search results).
The jump came from visitors from the second- and third-ranked countries of origin, made up, as far as I can see, from a rise in mobile rankings into the top 5 search results. The site is related to (and hosted in) the second-ranked country but not relevant to most mobile users in that country. The site is not related to (and not hosted in) the third-ranked country but would be particularly relevant to users from that country.
(The #1 country is the USA which saw very little change in rankings or CTR. It does seem to have some fairly wild swings in impressions from US desktop users but this may be due to office-based searches versus home searches.)

It means your site is now ranked on the merits of the mobile version.

Is this a daft question?

Is there an actual Google site where one can test the mobile SERPs?

For me testing mobile results seems to vary depending whether I am using Android, IOS or Windows.

If so, why is that?, Why deliver different SERPs, surely that means using unnecessary extra resources?

For me testing mobile results seems to vary depending whether I am using Android, IOS or Windows.
If so, why is that?, Why deliver different SERPs

Because Google had collected and compiled tremendous amount of data over the years. And from their analysis it's certainly showing that user of a mobile Windows, has a different profile and interactions, than a user of IOS or Android. Just look at those buying iPhones, and those taking an Android phone, you can see they are not the same kind of users. Google is certainly also delivering different SERPs based on the time of the day for the same reason.

@RedBar - Each person gets a different search result, albeit sometimes subtle.

AI returns search results using many metrics: your intent, search terms you used, search terms you've previously used, which results you've clicked through to, bounce rate, whether you are signed in, your previous search history, web pages you visited, your location, your browser, your OS, your IP, etc.

How all this is put together remains a mystery.

@RedBar - Each person gets a different search result, albeit sometimes subtle.

AI returns search results using many metrics: your intent, search terms you used, search terms you've previously used, which results you've clicked through to, bounce rate, whether you are signed in, your previous search history, web pages you visited, your location, your browser, your OS, your IP, etc.

How all this is put together remains a mystery.

Which is why when one reads all the people posting about how they are rising or falling in the "update"threads..and the ( usually "self proclaimed" , or proclaimed by their SEO friends ) "SEO "experts" hinting that they know what to do to make one #1 in SERPs for a keyword..

One cannot help but smile ;)

AI returns search results using many metrics

Ok, I get that however another question, how does Google profile me?

Any time I search, I am never logged-in, my cache is clear, no history yet they have my location, OS and IP, how do they treat me? Basically as a new user therefore I am getting their "cleanest" and most current results or are they just best guessing since, theoretically, they shouldn't know anything about me?

And from their analysis it's certainly showing that user of a mobile Windows, has a different profile and interactions, than a user of IOS or Android. [

Hmmm ... I primarily use Windows phones however I also do a lot of testing with Android and IOS and always use the same parameters when doing my tests and, yes, they do quite often deliver different results for the same query.

Surely this is a massive presumptuousness and manipulation on Google's side? I know for a fact that the way I use my Windows phone is completely different to many other Win users ... Or am I in a "club" Google chooses to deliberately ignore since they can't profile me?

Yes, I did realise that this has been going on for years but why is it some two+ years later of the so-called mobile index, that Google has still not managed to "complete" it?

Or is it 3+ years now?

I received an email that my main site was in the mobile index a month or so ago. Two more sites received notifications a week or so ago.

No noticeable change at all. But then again, I wouldn't expect it because the mobile and desktop versions are almost the same content.

We also received the mobile first email. Our content is the same mobile and desktop.

If some are submitting mobile optimised sites and ranking better because of it that causes us an issue, because, 90%+ of our visitors (B2B Technical) are desktop users and it looks likely to remain that way.

Still no notification for us. I nearly posted yesterday to report that the Mobile G Bot surge appeared to be over but they're back again this morning. Got the sleeves rolled up fixing and redirecting (very) old URLs now being reported as broken or "Soft 404" in the Smartphone section of GSC.
No significant ranking changes that we can detect so far, but there's just no way that rankings can be unaffected by this; our indexed page count has gone up 20% over the last week and G must have a much fresher snapshot of all our pages now, thanks to the crazy crawl rate.

As I mentioned somewhere else, I received the notification earlier this month, and since, traffic is in constant increase, especially from mobile devices, but also from desktop (and so does incomes)

Traffic have grown rapidly from mobile devices

I have seen a 20% drop in traffic after getting the Mobile First index notice a week ago. Only difference between two sites is an additional hamburger menu on the mobile version, while the desktop version has another menu system (which is still there but visibly hidden on mobile). Hoping that the drop is temporary. Anyone see a dip in traffic and then restoration? How long did it take.

Keep In mind that although you may have a responsive site, site speed is measured differently for mobile. So my thought is that desktop traffic could suffer from mobile one, if the mobile speed test fails, even if you got a good rating on your desktop speed.

No noticeable change at all. But then again, I wouldn't expect it because the mobile and desktop versions are almost the same content.

Exactly. If done correctly, there shouldn't be any change.

Your mobile site should contain the same content as your desktop site. The only thing that would be any different would be navigation and possibly some images that do not adjust to size very well. If you use ads, the placement may vary.

Just to update this... we got our "Mobile First Indexing Enabled" message from Google this morning - almost 4 months after the "mother of all Googlebot surges" that triggered this post! There have been a few small crawl spikes since, but nothing approaching the scale of last September.

We do have a large site (many thousands of pages) and have been responsive, with good page speed, for several years so would hope not to have any big issues from this - and so far, there doesn't seem to be any obvious effect either way.

So, if you do spot a crawl surge from the mobile G-bots; it may be months before anything happens!

We got the big crawl 11/3/18 and the mobile first index notice today. Aside from the notice, there have been no other discernible changes.

Where are you getting the mobile first indexing enabled message? Is it the email address registered under the Search Console? Is there a way to check to see if your site is mobile first indexed?

The message comes via email. I can't see any indication in the Console of whether or not a site is MFI.

I think I see it in the search console. Not explicitly but if you look at your site in the console, it tells you if it's the desktop or mobile bot that indexes it. It wouldn't make sense for the desktop bot to index a side that's mobile first and vice a versa. It matches what I'm seeing in the google search results. There are some differences between the desktop and mobile versions of my site. I don't see any of the desktop only things.

it tells you if it's the desktop or mobile bot that indexes it. It wouldn't make sense for the desktop bot to index a side that's mobile first and vice a versa

Be careful not to equate crawling and indexing. If a site is fully responsive, it doesn’t matter which robot does the crawling, as they will all receive the same content. In no case is the indexing done by the robot itself.

Cursory pawing through logs suggests that they’re currently running about 3:1 mobile (Android) : vanilla Googlebot, but this changes from month to month and from site to site. Once they’ve established that a site is responsive, it’s duplicated effort to keep crawling with both.