Fission is "conveniently" hard because two heavy, naturally co-occurring isotopes are nearly the same weight, and only the lighter one is spicy, and the capability of separating enough of them to be dangerous requires nation-state-level resources, and the supply chain of those resources has obvious choke points that we can use to make them less available. But there exist activities, which I understand to be quite bio-risky, that need such little equipment and expertise that it's info-hazardous to even talk about them. A single half-clueless technician could carry them out at an agent's direction. If your response is "thus, we should be worried about morally bankrupt researchers", I would agree, but I still think the risk increases as LLM agents get increasing amounts of control over wet lab equipment (whether via robotics or tele-operated humans).

> do you think Anthropic and OpenAI are going to put a filter on the LLM they sell to the US Military?

I don't think it matters, given the existence of strong open-weights models and the ease of post-training the guard rails away. Strong, bio-adventurous LLMs are imminently in the hands of much-less-reputable parties than the ones you describe. I think we are overall severely under-prepared to mitigate these risks, and could do much more.