I'm still seeing it, and it is tag-based, I believe. Changing the name seems to have made the links somewhat weird, though (it looks like both open_thread_march_14_march_20_2016 and open_thread_march_21_march_27 _2016 might work?).
Oh, it shows up on /r/discussion/new, but not on /r/all/recentposts.
Weird. I used to have a page that would redirect you to the latest open thread, finding it through the sidebar API. I took it down a month or so back because the API had vanished, but now it's apparently back.
The important part of the URL of this thread is /nf7/. The stuff after that is intended for human use, you can replace it arbitrarily.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.