Google has deprecated OpenID 2.0 and these services were shut down 20 April 2015.
What does this mean for your Sketchfab account?
We are migrating our "Log in with Google" feature to Google+ Sign-In (OAuth 2.0, OpenID Connect). This is planned for mid-March.
After migration, attempting to login with a Google account that does not have a Google+ profile will prompt you to create one.
If you do not use Google to login to Sketchfab, you will not notice anything.