Old Reddit is posts from before something like 2009. You now have to login to view Old Reddit.
https://old.reddit.com/login/?reason=lor2&dest=https%3A%2F%2...
It's not that important of a loss in the grand scheme of things. It's probably less than 1% of the posts that have ever been made on the Reddit website, since Reddit was a pretty small and obscure website until 2011 or 2012.
But it might be the first step toward making all of Reddit only readable with an account.
All of the redlib instances still work, and I believe they use the .json endpoint off of old.
What? No this is completely incorrect. old.reddit is a way of viewing reddit with the old (in my opinion far superior) UI, but includes new posts and comments. As for whether or not it requires an account, that appears to be something that they are A/B testing.
> Old Reddit is posts from before something like 2009
No, it works for the entire post database. If you have a login and go to the main old.reddit.com page you'll see current posts.
Edit: Er, that's how it used to be. Looks like it just redirects to the main domain now. RIP.