Adobe this week gave Mac users an early heads up that the next major releases of Lightroom and other Creative Cloud desktop apps will only run on OS 10.10 (Yosemite) and later versions. They gave no indication of when the next major release of Lightroom will come out.
If you’re running 10.9 or earlier, you can update now to 10.11 (El Capitan), or wait until after September 20 and update to 10.12 (Sierra) when it’s released. (Check to see if your computer will run: El Capitan Sierra at this link.) I don’t recommend updating to Sierra until it has been out for a while, since there are often early issues with Lightroom compatibility. From what I understand, most of the compatibility issues with El Capitan have been worked out.)
Mac OS updates are free. To see which version you’re running, click on the apple icon in the top left and choose About this Mac. To get to the Update page, from this same screen click on Software Update.
If you choose not to update, you will still be able to continue to use Lightroom 6 / CC 2015 and the current versions of other CC desktop applications.