Is Scalable Link Interface (SLI) supported in Vulkan?
Two extensions were introduced after the release of Vulkan 1.0 to allow SLI-style rendering. The extensions are VK_KHR_device_group and VK_KHR_device_group_creation. At the time of the Vulkan 1.1 release, these extensions were pulled into core Vulkan. More info can be found in this Stack Overflow issue.