In this question, I am assuming the meaning of 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 any other texts