As of today, NVK is now a conformant Vulkan 1.3 implementation on Turing (RTX 2000 and GTX 1600 series), Ampere (RTX 3000 series), and Ada (RTX 4000 series) GPUs.
NVK itself is not dependent on anything proprietary, but it's practically required to enable NVIDIA's GSP firmware blob if you want to see actual performance since it's what enables re-clocking (older post by Collabora here which touches on it).
Slight correction, it's available in Linux 6.7, and has to be enabled with the kernel parameter nouveau.config=NvGspRm=1. It may be enabled by default soon though (latest news I could find about that here).
NVK is a new fully open source driver for Nvidia GPUs. Derived from documentation & official FOSS code drops from Nvidia, unlike the legacy Nouveau driver which was mostly the product of reverse engineering proprietary drivers.