I think the case for it under a symmetric person-affecting view (like presentism or necessitarianism) is much weaker compared to, say, global health and poverty work, for which we have far more robustly cost-effective interventions.
Two analyses here indicate expected cost per life saved in the present generation from both AGI safety and alternative foods for nuclear winter, abrupt climate change, etc to be lower than global health. There are orders of magnitude of uncertainty in the X risk interventions, but still little overlap with the global health cost effectiveness distributions, so I think it is fairly robust.
This previous post by Gregory Lewis also seems relevant both to this point in particular, and to this post in general. E.g., Lewis writes:
there is a common pattern of thought along the lines of, “X-risk reduction only matters if the total view is true, and if one holds a different view one should basically discount it”. Although rough, this cost-effectiveness guestimate suggests this is mistaken. Although it seems unlikely x-risk reduction is the best buy from the lights of a person-affecting view (we should be suspicious if it were), given ~$10000 per life year compares unfavourably to best global health interventions, it is still a good buy: it compares favourably to marginal cost effectiveness for rich country healthcare spending, for example.
Second, although it seems unlikely that x-risk reduction would be the best buy by the lights of a person affecting view, this would not be wildly outlandish. Those with a person-affecting view who think x-risk is particularly likely, or that the cause area has easier wins available than implied in the model, might find the best opportunities to make a difference. It may therefore supply reason for those with such views to investigate the factual matters in greater depth, rather than ruling it out based on their moral commitments.
By robust, I mean relying less on subjective judgements (including priors). Could someone assign a much lower probability of such catastrophic risks? Could they be much more skeptical about how much extra work in the area reduces/mitigates these risk (i.e. the progress)?
On the other hand, how much more skeptical could they be of GiveWell-recommended charities, which are based on RCTs? Of course, generalization is always an issue.