Old Tibetan, also called as "Imperial Old Tibetan" was an ancient form of Tibetan that was used during the era of Tibetan Empire from 7th to 9th Century CE. It is earlier than Classical Tibetan and Modern Tibetan.
The Tibetan Empire at its peak time(810s-830s CE), controlled almost the whole western part of contempory China and beyond, rivalling with the Tang Dynasty at the east which was on the downhill path. However, the Tibetan Empire fell into civil war at the middle of 9th Century CE and lost its influence to the surrounding regimes eventually.
In 816, during the reign of King Sadnalegs, literary Tibetan underwent a thorough reform aimed at standardizing the language and vocabulary of the translations being made from Indian texts, which was one of the main influences for literary standards in what is now called Classical Tibetan which is believed to come into being in 11th Century CE.Due to the reform, the Old Tibetan has many features that are lost in modern Tibetan.
CEUS at IU offers the course "Imperial Old Tibetan" occasionally and it is now available again in Fall 2021.