https://www.pcgamer.com/pubgs-savage-map-returns-for-testing-next-week/

At one-quarter the size of Miramar and Erangel, PUBG's Savage map is its smallest battleground yet. Evan, Chris and Jody reckon this is a good thing—but you can decide for yourself when it returns to test servers next week. 

As outlined in this Steam Community post, Codename: Savage enters its Closed Experimental Server on Monday 16 at 6pm PST/Tuesday 17 at 2am BST, and is live till the same time on Wednesday 18. Developer PUBG Corp will reopen its signup website this weekend, but those who claimed keys last time are good to go here.