Magadhi Prakrit
Assamese originated in Old Indo-Aryan dialects, though the exact nature of its origin and growth is not clear yet. It is generally believed that Assamese and the Kamatapuri lects derive from the Kamarupi dialect of Eastern Magadhi Prakrit though some authors contest a close connection of Assamese with Magadhi Prakrit. Assamese developed from Indo-Aryan settlements of Kamarupa—in urban centers and along the Brahmaputra river—surrounded by Tibeto-Burman and Austroasiatic communities. Kakati's (1941) assertion that Assamese has an Austroasiatic substrate is generally accepted – which suggests that when the Indo-Aryan centers formed in the 4th-5th centuries CE, there were substantial Austroasiatic speakers that later accepted the Indo-Aryan vernacular. Xuanzang, the 7th-century Chinese traveler, observed that the Indo-Aryan vernacular in Kamarupa had differentiated itself from the original vernacular before it did in Bengal. These changes were likely due to non-Indo-Aryan speakers adopting the language. The newly differentiated vernacular is evident in the Prakritisms present in the Sanskrit of the Kamarupa inscriptions from which Assamese eventually emerged.