This incident has been resolved. All gems should be included in the versions API again.
Posted 18 days ago. Jan 01, 2019 - 14:26 UTC
A fix has been implemented and we are monitoring the results.
Posted 18 days ago. Jan 01, 2019 - 14:19 UTC
We have received reports of some gems not being able to be installed. We have identified the issue and we are working on resolving it. Gems published before 2015-08-23 may be unlisted on the versions API.