On HN here, we've spent the last few years talking and thinking a lot about LLMs, so the paper might not include much that would be surprising to math-curious HN'ers. However, there is a large cohort of research mathematicians out there that likely doesn't know much about modern AI; Terence is saying there's a little utility in last-gen models (GPT-4), and he expects a lot of utility out of combining next-gen models with Lean.
Again, not surprising if you read his blog, but I think publishing a full paper in AMS is a pretty important moment.