Samsung has released official Android 5.0 Lollipop for Galaxy Tab S tablets. It is for the SM-T805 and SM-T800 variants. If you have not received it for your tablet, you can flash it from below given links. Just keep in mind that it will delete any file you have stored on the tablet.
The new Android 5.0 Lollipop update for the SM-T805 and SM-T800 brings plethora of performance improvements, security enhancements and bug fixes. You also get a new lock scree, improved notification bar and updated Touch Wiz user interface.
SM-T800 Wi-Fi firmware details
Model Name: Galaxy Tab S 10.5
Model: SM-T800 (Wi-Fi)
Country: France (XEF)
Version: T800XXU1BOCC
OS: Lollipop
OS Version: 5.0.2
Build Date: March 17, 2015
Changelist: 4403645
PDA: T800XXU1BOCC
CSC: T800OXA1BOC4
SM-T805 LTE firmware details
Model Name: Galaxy Tab S 10.5
Model: SM-T805 (LTE)
Country: Czech Republic (Vodafone)
Version: T805XXU1BOCC
OS: Lollipop
OS Version: 5.0.2
Build Date: March 17, 2015
Changelist: 4403645
PDA: T805XXU1BOCC
CSC: T805VFG1BOC4