Tom Klein’s last day at Sabre will be Dec. 31, when he will resign from his posts as CEO and member of the board. The announcement comes six months in advance to give the company time to hire a successor without disrupting growth plans, he said in a statement. He had worked for American Airlines when it was part of AMR and then switched to AMR’s Sabre unit. Sabre separated from AMR in the ’90s, and Klein became Sabre president in 2010 and CEO in 2013.