There hasn't been many changes to Google+ Sign-In since it's launch almost ten months ago, but today, Google announced three new improvements which should make it easier for both users and developers to use Google authentication in mobile and web apps. It may also lead to the further closing of the social login gap between Google+ and Facebook.
1. Support for all Google Account types
Google+ Sign-In will now support users with all Google account types including those that have a Google Apps account or a Google account that hasn't yet been upgraded to Google+. This will be great to allow more users to use Sign-In. Of course, there might not be as good of an experience if they aren't using a Google+ account.
2. Easy migration from other auth methods
This one is more for the developers that want to set up Google+ Sign-In on their app. It allows those that are using OpenID v2 or OAuth 2.0 Login to upgrade easily to Google+ Sign-In and take advantage of the additional goodies that it brings including over-the-air installs, interactive posts, and cross-device sign-in. It's also now fully compatible with the OpenID Connect standard. For more information, check out the sign-in migration guide.
3. Incremental auth
The third and final improvement is incremental auth, a new way to ask users for the right permission scopes at the right time instead of asking for all of it at once. For example, an app can now ask for just basic profile information at the beginning and then ask for further permissions like access Google Calendar or posting to Google+ later. This change will reduce friction to using an app, and it might also increase app sign-up completions and app engagement.
See below for a video explaining it a bit more: