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Z1 Battle Royale (formerly H1Z1 and King of the Kill) is a free-to-play battle royale game developed and published by Daybreak Game Company. The game's development began after the original H1Z1 was spun off into two separate projects in early 2016: H1Z1: Just Survive and H1Z1: King of the Kill. The games were further split as separate projects in October 2017, with Just Survive dropping the H1Z1 name, and King of the Kill becoming simply H1Z1.
After three years of being in early access for Microsoft Windows, H1Z1 officially released as a free-to-play game on February 28, 2018, later released for the PlayStation 4 on August 7, 2018. A month later however, development of the game was transferred to NantG Mobile, who attempted to revert the game back to an earlier build from 2017, rebranding it as Z1 Battle Royale. In April 2019, development of the game was given back over to Daybreak.
Source: Wikipedia, "Z1 Battle Royale", available under the CC-BY-SA License.