I know this change already took place some months ago, but I wanted to write about this now. Here's the situation:

• When I click on
• I login on my Gmail account and get :but in my case, if I click onAccept then I'm forced to upgrade to a Google profile because of the new Stack Exchange OpenId login behaviour.
• If click onAnnuler(cancel) I get :

I created a Gmail account in the early beginning, I only had to fill in the password, name, and email address. I also find unfair that others providers don't have to provide this information while it is required for Google.
I can understand this for things like Facebook... But, not every Google account is a Google profile...

Also, let's be clear:

• No, I will never upgrade, the same way I would never create a social media profile.

• Do not try to convince me it's Google, because the message states the contrary and it perfectly work if I login using those other ways :

Update:

Ok, you are not using OpenId but Google+ Sign in (which is not really OAuth 2.0). According to the documentation, there are two endpoints, and using https://www.googleapis.com/auth/plus.login instead of https://www.googleapis.com/auth/profile prompt users to upgrade to a Google+ profile even if you only require an email address.
Anyway Google clearly states it : "Your app can either prompt those users to create a Google+ profile or not...", which means that Google requires you to upgrade to a Google profile only if requested (I don't really know who to believe but I'm open to discussing it).