Micron is showing DDR4 memory at the Consumer Electronics Show this year. The company had a DDR4 demo last year, too, and the new one isn't much different. However, the next-gen memory type is closer to market, and the company shared some details about when we can expect the first modules.
DDR4 memory for servers will start selling in the spring. The initial modules will target early adopters, and they'll be available directly from Crucial's website, among other sources.