Allegedly it's the 690, they claim it will be launched before May 5th.
There's still essentially zero availability on the 680's, so I don't know how they expect to stock dual GPU cards.
It turns out that the cryptic picture posted on NVIDIA GeForce Facebook page indeed is a teaser for NVIDIA GeForce GTX 690, a dual-GPU graphics card based on two GK104 GPUs. Several independent sources told SweClockers that NVIDIA is preparing to launch this SKU "in the week beginning April 30," i.e., no later than May 5. It is quite possible that NVIDIA launches it on the 30th, to share the limelight with Intel's new 3rd Generation Core "Ivy Bridge" processors, which will be released to market on the 29th. The card will feature a total of 3072 CUDA cores, and 4 GB of GDDR5 memory. We haven't heard much about its competitor, the Radeon HD 7990.