SEC Commissioner Piwowar, whose term officially ends on June 5, 2018, announced his resignation on the earlier of July 7th or the swearing in of his successor. His statement notes:
Over the next two months, I will continue to work steadfastly with my fellow commissioners and SEC staff to advance our important mission of protecting investors, maintaining fair, orderly, and efficient markets, and promoting capital formation.
Commissioner Stein's term expired June 5th of last year; however, commissioners may (and commonly do) serve up to 18 months beyond the expiration of their terms. This WSJ article observes: "In theory, the White House and Senate could move quickly and nominate replacements for both Mr. Piwowar and Ms. Stein. The Senate usually considers candidates for commissioners in pairs -- one Republican and one Democrat."