Zuck has made it clear this is a Pascal's Gamble:
"If we end up misspending a couple of hundred billion dollars, I think that is going to be very unfortunate, obviously. But I actually think the risk is higher on the other side . If you build too slowly and superintelligence is possible in 3 years, but you built it out assuming it is possible in 5 years, then you are out of position on the most important technology."
His assumption is that superinteligence is close, its just a question of whether it is 3 or 5 years!
No, the first sentence makes it clear that he is aware AGI is not a given. His position is that there is a possibility we can reach super intelligence, and given that possibility they want to be on the bleeding edge and are investing accordingly, given that even total failure won’t cripple their business and all their competitors are doing the same.
"If you build too slowly and superintelligence is possible in 3 years, but you built it out assuming it is possible in 5 years, then you are out of position on the most important technology"
This made me think Zuck sees it as a question of when rather than if. I.e its more a question of 3 vs 5 years rather than possible vs non possible.