They try to train the model to not answer “wrong”. But as we know, LLMs are not completely reliable and they can ignore their training. So to be sure, you need something that looks at the actual output and decides whether it’s ok, either with a dumb text search like old school filters, or perhaps with a second (likely smaller) language model.

The output needs to have been written for those post filters to act on it, so if it shows the output in real time, you see it!