Some evidence about this: Eliezer was deliberating holding off on publishing TDT to use it as a test of philosophical / FAI research competence. He dropped some hints on LW (I think mostly that it had to do with Newcomb or cooperating in one-shot PD, and of course people knew that it had to do with AI) and also assigned MIRI (then SIAI) people to try to guess/reproduce his advance, and none of the then-SIAI people figured out what he had in mind or got very close until I posted about UDT (which combined my guess of Eliezer’s idea with some of my own and other discussions on LW at the time, mainly from Vladmir Nesov).
Very interested to hear this history!