Harry Truman was the last president to call a special session of Congress in 1948. The power exists but modern presidents haven't needed it because Congress stays in session most of the year.
Article II gives the President authority to call both chambers or just the Senate into special session for urgent business when Congress is adjourned. Presidents have used it 46 times to recall only the Senate and 28 times to recall both chambers. Congress now uses pro forma sessions—brief meetings every few days with no business conducted—to technically stay in session even during breaks. This prevents the President from making recess appointments and eliminates the need for special sessions. The power remains available for genuine emergencies, but the way Congress manipulates its schedule has made it effectively obsolete.