The release of Mental Ray is discontinued as of 20 November 2017. NVIDIA will no longer offer new subscriptions to the Mental Ray plugins for Maya and 3ds Max, as well as Mental Ray Standalone, – is stated on the developer’s website. The support and software updates for current customers who have purchased the licenses will be continued for the remainder of their subscription terms. There will be maintenance releases with bug fixes throughout 2018, they will also add support for the upcoming NVIDIA Volta™ GPU generation.
The official reason for this decision is the change of the priorities. NVIDIA will focus on bringing GPU accelerated ray tracing technology to other rendering products and it further invests in core rendering technology, like NVIDIA OptiX and real-time ray tracing platforms for next-generation GPU
architectures; MDL, the open Material Definition Language; NVIDIA IndeX, the platform technology for visualization and computing of multi-valued
volumetric and embedded geometry data; NVIDIA Iray for physically based rendering platforms focusing on the CAD, product and architectural design markets.
More information on manufacturer’s website here