Steve Bannon is now under subpoena by both House investigators and the Special Counsel after he refused to answer questions before Congress. Following a problematic pattern of current and former Administration figures, Bannon reportedly did not invoke executive privilege (which must be asserted by the White House) but refused to answer questions about his work on the transition team and White House. There is no basis for such a broad assertion of executive privilege and, unless Bannon changes course, he could be looking at contempt sanctions down the road. Despite his refusal to cooperate with the committee, he has reached a deal to speak with the Special Counsel investigators outside of a grand jury.
Update: The White House is now asserting that there were prior discussions with the Committee and the Committee violated the agreement on scope. Notably however the agreement was to discuss only matters from the campaign and not the transition or White House periods. That would be an astonishingly limited scope for the Committee staff to agree to given the material events after the campaign, including the time periods covered by statements made by Bannon in the Wolff book.