Yes, they can. Meta described a clever way in their paper on training Llama3 [1] (in section about factuality).
The idea is to sample several answers to a question that you know the answer to. Let an LLM decide if the given answers are different from your known truth. If so, you found a question, that you can train your LLM in the next post-training round to answer with "I don't know".
Do that a couple hundred of times and your LLM will identify neurons that indicate doubt and from here on have the ability to answer with "I don't know".
[Edit] The article here also mentions a paper [2] that comes up with the idea of an uncertainty token. So here the incorporation of uncertainty is already baked in at pre-training.[/Edit]
[Edit] The article here also mentions a paper [2] that comes up with the idea of an uncertainty token. So here the incorporation of uncertainty is already baked in at pre-training.[/Edit]
[1] https://arxiv.org/pdf/2407.21783 [2] https://openreview.net/pdf?id=Wc0vlQuoLb