Apple issued two updates for late 2013 iMacs on Thursday, iMac SMC Firmware Update 1.1 and iMac 10.8.5 Supplemental Update 1.0. The first addresses an issue with Power Nap, while the second deals an external drive issue and a problem with some USB Bluetooth adapters.
Apple's 2013 iMac Line
iMac SMC Firmware Update 1.1 (921KB download)
This update is recommended for iMac (late 2013) with flash-only storage. This update improves the Power Nap feature in Mavericks on your flash based iMac by allowing it to perform silently, without spinning up the fan.
Power Nap periodically updates apps, such as Mail, Contacts, and Calendar, and will download software updates while your iMac is sleeping.
iMac 10.8.5 Supplemental Update 1.0 (17.11MB download)
The iMac OS X v10.8.5 Supplemental Update 1.0 is recommended for iMacs (Late 2013) using NVIDIA GeForce GT 750M graphics and running OS X Mountain Lion v10.8.5.
- Fixes an issue that may cause external drives to be ejected after the computer goes to sleep
- Fixes an issue that may prevent certain USB Bluetooth adapters from working
You can use the links above for standalone updaters. Alternately, check the Mac App Store under Updates.