Recently, I had a conversation with someone from a math background, asking how they could get into AI safety research. Based on my own path from mathematics to AI alignment, I recommended the following sources. It may prove useful to others contemplating a similar change in career:
You mileage may vary, but these are the sources that I would recommend. And I encourage you to post any sources you'd recommend, in the comments.
I guess I'd recommend the AGI safety fundamentals course: https://www.eacambridge.org/technical-alignment-curriculum
On Stuart's list: I think this list might be suitable for some types of conceptual alignment research. But you'd certainly want to read more ML for other types of alignment research.
I also found this thread of math topics on AI safety helpful.