We reported back in June that El Capitan beta 2 seed included assets and code references to a rumored 4K 21.5 inch Retina iMac, which would accompany the 5K 27 inch Retina iMac in the family. El Capitan beta 6 was released last night and also includes some juicy references to the as-yet-unannounced 21.5 inch Retina Mac desktop.

Consomac has digged around the OS X seed and found that Apple has included metadata for a 4K iMac screen.  The file says the iMac has a native screen resolution of 4096×2304 as well as several ‘scaled’ sizes like other Retina Macs. The icon attached to this file looks identical to current iMacs which indicates that the new iMacs will not have noticeable exterior design changes.

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The monitor definitions also include references to a couple of new 5K iMacs. This gels with a report from KGI yesterday which claimed Apple is readying iMacs with improved screen technology and internal improvements to components.

In general, the iMac is due for a refresh so an update of some kind is expected. Most models in the iMac lineup have not been updated since late 2013. It now seems almost certain that a 4K Retina 21.5 inch iMac is on the horizon.

With these references appearing in El Capitan, it currently seems like the 4K Retina iMac will ship with Apple’s new OS although it is possible for Apple to patch support into Yosemite. However, the company has a history of releasing new Mac hardware alongside new versions of the operating system.