It starts at $1,800, £1,749 or AU$2,699.
The new upgrades include new Intel CPUs, faster graphics, better storage and new ports.
The 2017 27-inch iMac is equipped with a seventh-generation Intel Core i5 or i7 processor.
In addition to four older Type-A USB 3.0 connectors (up from three), two new Thunderbolt 3-enabled USB-C connectors replace the two previous Mini Display Port connectors. It keeps the Ethernet RJ-45 jack, SD card slot and headphone jack as well.
The design retains the now-unfashionable fat bezels around the display.
You can still upgrade the memory, but that's about all that's easy to get to.
For connectivity, the updated iMac incorporates Bluetooth 4.2 as well as the previous options.
The display measures brighter than the earlier model, and now covers the P3 color gamut for consistency across Apple's most recent screens.
Now that it incorporates the latest Radeon 500 series graphics processors, it can drive more than a single external display in addition to the built-in one.