Updated models with AMD graphics options expected in early 2017.
Evidence that Next iMacs and Mac Minis to use NVIDIA Chipsets
Apple will apparently be bringing these improvements to both the new iMac and Mac mini. While many have expected the iMac to receive these upgrades, the fate of the Mac mini has been less certain.
A configuration file found in the Mac OS X version that ships with the new MacBook and MacBook Pros reveal entries referencing unreleased "MacMini3,1" and "iMac9,1" models. The relevant lines have been excerpted here:
The CFG_MCP79 appears to refer to the NVIDIA MCP79 chipset, which suggests these unannounced models will use this new chipset. The currently shipping iMac and Macmini carry model numbers of iMac8,1 and Macmini2,1. The findings were originally described in a forum post that we've subsequently verified. The references are found in System -> Library -> Extensions -> IOPlatformPluginFamily.kext -> Contents -> PlugIns -> ACPI_SMC_PlatformPlugin.kext -> Contents -> Info.plist in the new MacBook or MacBook Pro.