PUBG Corp are continuing the testing on Codename: Savage on 16 April 2018 for USA and on 17 April 2018 for Europe and Asia. They have released more details and changes since the last testing run, as a heads up for potential testers.
PUBG's new map is coming back for another round of testing so if you missed out on it the first time, you can jump in on 16 April 2018 at 6PM PDT if you're in USA or 17 April 2018 at 2AM GMT for Europe and 10AM KST for Asia. The second run will conclude on 18 April 2018 6PM PDT for USA, and 19 April 2018 for Europe and Asia, at 3 AM GMT and 10 AM KST, respectively.
In case you didn't make an account for Closed Experimental Server the first time around, you can get one from this link. There is a limited number of keys, but at the time of writing, there were no reports of them running low or being depleted. Players who already have an account only need to sign in again, no need for further registration.
Savage has received several changes since the last test run, including both the red zone and the blue zone. Red zone's size and duration have both been decreased to better fit the map's size and the blue zone now adjusts its waiting time based on the number of players left standing.
Grenades will now spawn more often and 8x scope can now be obtained, but only from care packages. Boat spawns have been decreased across the board but their spawn points have been moved to more intuitive places, like along the towns that are close to the sea.
Before jumping to PUBG Corp's future plans, here are full patch notes. Codename: Savage will reportedly not be released for another few months but it will have more testing runs in the future. This testing with players is apparently the way PUBG Corp want to test any new content that's going to be released in the future as the player feedback from Savage's previous test run proved to be highly beneficial.