Upanishadas are often called Vedanta. Why?
The main motto of the Upanishads is “Knowledge Awards Salvation”. Upanishads are called Vedanta (the end of the Veda) firstly, because they denote the last phase of the Vedic period and secondly, because they reveal the final aim of the Veda. The Oldest Upanishads are Brihadaranyaka and Chandogya Upanishads which date as back as the first millennium BC. Latest were composed in the medieval and early modern period. The latest Upnishad is Muktikā Upnishad and was recorded by Dara Shikoh.
E-Book: 002 - Indian Literature