Standalone battle royale spin-off Dying Light: Bad Blood will arrive on Steam Early Access in September. The Early Access release will be for PC players only but Bad Blood will be a multiplatform PC and console (presumably PlayStation 4 and Xbox One) game upon full release.
When full release is, however, is unclear, but there's a line in the press release which suggests the Early Access could last three months. "The $19.99 Founder's Pack provides in-game currency and exclusive items, including the Founder's Pass that will deliver three Legendary skins throughout the three months following the Early Access launch," it says.
The $20 Founder's Pack is what you need to buy to join the Early Access phase, although when Bad Blood eventually launches it will be free-to-play. Various maps, modes and items will be added throughout Early Access.
Bad Blood is battle royale for 12 people against both each other and the zombies which characterise Dying Light. You'll scavenge for weaponry and equipment, as in other battle royale games, but you'll level up too, and use Dying Light's speedy parkour traversal to whizz around the rooftops. Only one player can get to the chopper, as Arnie would put it.
Before Early Access opens there will be two global playtest phases which you can sign up for (until 22nd August) on the Dying Light: Bad Blood website. The first runs Saturday 26th August to Sunday 27th August (5pm-5pm BST), and the second runs Saturday 1st September to Sunday 1st September (5pm-5pm BST).