Unsurprisingly, there's another big change on C9 (for classic users) without any announcement.
Honestly, I've never been to a forum where admins are so hostile to their own users.
If you had a classic C9 login, and you logged out, on the next login, you'll see this:
Notice how the option to use classic logins is gone... After using your passport, you'll get:
Yep, it's officially gone.
(Sampy Ninja Edit: Just wanted to tweak the title so people had the full info)