We know it's coming, but it's just a matter of when. NVIDIA is preparing the GeForce GTX 980 Ti that should better counter the upcoming Radeon R9 390X from AMD, with a full GM200 core.
The GM200-powered GeForce GTX 980 Ti should be released in September, a couple of months after AMD's launch of the Radeon R9 390X which is expected to happen during Computex in June. There are some suggestions that NVIDIA would spoil AMD's fun during the R9 390X launch, so we could see a big announcement before, during or after Computex from NVIDIA.
NVIDIA's GeForce GTX 980 Ti should be close to identical to the behemoth that is the GeForce GTX Titan X, but knock down its VRAM from 12GB to 6GB. We should also see AIB partners free to slap on aftermarket coolers, which didn't happen with the Titan X, which is going to open up a can of whoop ass on the market.