Yes – but only in the 27″
See here – LINK
The 21.5-inch iMac comes with 8GB of memory and can be configured online with 16GB. On the 27-inch iMac, 8GB of memory comes standard, and you can upgrade to 16GB or 32GB. Configure and buy your iMac at the Apple Online Store and it will arrive with the memory already installed. Or add more memory to the 27-inch model yourself by popping open the easy-to-access memory panel on the back.