Nvidia extensions for their own GPUs? So how do other GPUs which don't share the same design work then?
Why do you think AMD and Intel are working with Khronos Group - they are adding their own extensions so their own GPUs will work.
I would imagine it's Microsoft who did most of the software heavy lifting work and only worked with Nvidia as they had the first compatible hardware.
Edit!!
The whole point of Nvidia Windows extensions under DXR is so it can use Nvidia specific RT hardware. If not it will fall back to software only rendering which is agnostic.
So are people saying basically DXR is essentially mostly Nvidia work and MS put their own branding on it? Because I would find it weird if MS would like it's work shared with a competing API.
You dont seem to understand what an API is? The Nvidia extensions are essentially just method names and variable signatures. How that interacts with the hardware is entirely up to the driver, as such the API is hardware agnostic as long as it supports the same underlying functionality.
Microsoft and Nvidia worked together on the DX12 ray tracing API called DXR with minimal external input as AMD had no hardware.
MS have no real control over what the Kronos group decides in terms of API. You can only patent and copyright specific implementations, not vague ideas. An API is just a naming convention with a contract to provide the specified functionality. Much of the Vulkan and DX12 API is very similar if not identical by design. E.G the HLSL shading language used by vulkan is the exact copy of Microsofts DX12.1. The raytracing API mostly exists as functions in the HLSL shader language. This allows cross-API functionality and makes it easier for devs to move from DX12 to Vulkan or support both APIs.
And thus ray tracing in Vulkan will resemble MS DX12 DXR which is largely designed by Nvidia.
If AMD require wildly different API then they will have to work with MS to develop a new API and they wont be DXR compatible. That would be quite a failure for AMD in the short term and unrealistic. What is more likely is AMD will first produce DXR compatible hardware and confirm to the API largely proposed by Nvidia. In the future AMD will have a larger say in necessary changes. Short term they can specify different feature sets
None of this is particularly bad for AMD. Ms will have only accepted Nvidia's API suggestion if they believed it was fairly hardware agnostic and a sensible API.