[simonw]

The problem with hallucinations is that they really are an expected part of what LLMs are used for today.

"Write me a story about the first kangaroo on the moon" - that's a direct request for a hallucination, something that's never actually happened.

"Write me a story about the first man on the moon" - that could be interpreted as "a made-up children's story about Neil Armstrong".

"Tell me about the first man on the moon" - that's a request for factual information.

All of the above are reasonable requests of an LLM. Are we asking for a variant of an LLM that can flat refuse the first prompt because it's asking for non-real information?

Even summarizing an article could be considered a hallucination: there's a truth in the world, which is the exact text of that article. Then there's the made-up shortened version which omits certain details to act as a summary. What would a "hallucination free" LLM do with that?

I would argue that what we actually want here is for LLMs to get better over time at not presenting made-up information as fact in answer to clear requests for factual information. And that's what we've been getting - GPT-5 is far less likely to invent things in response to a factual question than GPT-4 was.

[janalsncm]

> What would a "hallucination free" LLM do with that?

To me, there’s a qualitative question of what details to include. Ideally the most important ones. And there’s the binary question of whether it included details not in the original.

A related issue is that preference tuning loves wordy responses, even if they’re factually equivalent.