Something weird is happening with LLMs and chess

I remember one of the early "breakthroughs" for LLMs in chess was that if it could actually play legal moves(!) In all of these games are the models always playing legal moves? I don't think the article says. The fact that an LLM can even reliably play legal moves, 20+ moves into a chess game is somewhat remarkable. It needs to have an accurate representation of the board state even though it was only trained on next token prediction.