These Senate hearings are not jovial chats among friends. They are in the same ballpark as depositions, or interviews with law enforcement officiers. You are not there to make the opposition’s work easier. (Assuming you with counsels decided that the best option for you/your company is to appear.) You have to be curteous, and truthfull. But you absolutelly should not go into “guessing what the question might be”.
When he asks “Will you commit ending finsta?”
I would answer “At facebook we have no feature or setting named finsta. We cannot commit to end what we don’t offer.” And let him explain what he thinks finsta means to him.
In casual conversations we often try to answer the question we think we should have been asked. This is not such an occasion.