Yichud before marrige

Dear Rabbi, If an unmarried man and woman have yichud together, with witnesses, do they need a get? What about without witnesses? If no, are there any cases at all where a get might be required? Thank you very much

Shalom U'veracha, While yichud is very serious and one should be very careful not to be secluded with a woman, if they were in yichud even with witnesses they do not need a get. Only in the case where a man gave a ring and said the formula "Harei at mekudeshet li etc." are they considered married and need a get. If a man had relations with a woman after making a similar declaration and witnesses saw the relations, an almost impossible case, then they would also need a get. Kol Tuv,