In this question, I am assuming the meaning of the words caste, Varna, class stands for same. Don't consider tribes as same as caste.
Consider the following talks by Krishna in Mahabharata
Krishna said, '...Thou must, O Sanjaya, take into thy consideration the division of the four castes and the scheme of respective duties allotted to each. ...'
From the Bhagavad Gita 4.13
"The Holy One said,--'.....The quadruple division of castes was created by me according to the distinction of qualities and duties. ....'
Does Krishna talk about any other statement beyond this four-class system such as out of the caste system, 5th caste, etc., anywhere in Mahabharata or in any other texts?