Chess.com has rules as nearly like OTB as possible. OTB you have to claim a draw, same thing here; it is not automatic. Check this article out on how to claim a draw:
https://support.chess.com/customer/portal/articles/1444798
repetition of moves
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more than once, the last game I played, the system does not assign a draw by repetition of moves ... I do not understand ... does it work?
look at this game...
http://www.chess.com/livechess/game?id=883857152
it is clearly repetition of moves...