Given the same inputs but not provided the results (output) from our accountant, did it come to the same conclusions or have good analysis as to why it differed?

Obviously, accounting is "spreadsheet math" intensive, so Claude wrote some python scripts for that which kept the math very stable. But there were some complex nuances that had taken the accountant and I quite a bit of work to track down and clarify. Claude quickly had a very accurate read on the situation and knew all the right clarifying questions.

I'm not yet ready to ever sign a return that's been entirely AI prepared, but I left the exercise pretty impressed.