Sincerity? I don't know. He seems to really believe in AGI and the singularity and all that, but everything else seems to be lie after lie. This article [0] on the New York Magazine paints him as an incredibly insencere manipulator, which lines up with accusations made by Helen Toner and others. Things he repeatedly says (not caring about money, caring a lot about safety) are often at odds with his actions.

https://nymag.com/intelligencer/article/sam-altman-artificia...