With the new optimisations, the app will be able to run on Android devices running version 4.0.3 up to 5. This new update has started rolling out worldwide in a staged manner.
What is interesting about this new update is that Skype claims that it will be "lighter on both disk and memory consumption" which will allow it to run with "greater speed and better audio and video quality" on the 'lower end Android device'. This will also result in better performance of the app at places where network connectivity is not ideal.
You don't need to panic if you can't see the update yet, as it will gradually reach to everyone.
This may be Microsoft's attempt at updating the app to an approach similar to Android Go where all the major apps are optimised to run by using less amount of storage and memory while enhancing the overall user experience.
One thing to note here is that this is not the only optimised version of the app as the company had already launched Skype Lite more than a year back. The only difference here is that Skype Lite is limited to the Indian market along with the focus of chat and sharing.