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.