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I made a post in another thread but this might needs its own topic.
In the Arnold documentation, it mentions supported GPUs include the 980 Ti, 980, 970, 960, 950.
https://docs.arnoldrenderer.com/display/A5ARP/Supported+Graphic+Cards
However, Arnold GPU also requires the Creator Ready Driver, but checking out Nvidia's blog, I see no mention of the Maxwell architecture, nor does it appear downloadable for them.
https://blogs.nvidia.com/blog/2019/03/20/rtx-creator-ready-drivers-supercharge-apps/
GeForce 9000 is a Maxwell series card, and that's supported by Optix. And Optix is what Arnold GPU uses.
I expect the drivers will be made available in the next few days.