Very soon you will notice a change to the sign in page for your Google account. You will sign in the way you have always signed in--your username and your password will not change. What will change about the sign in page? The sign in page will have a much cleaner, simpler look. The sign in process will be faster and it will be consistent across computers, phones and tablets.
The new sign in page will be happening soon, so be on the look out for it.