The Rangers apparently recalled Erasmo Ramirez before today's game, and optioned Justin Thompson back to AAA.
Because Thompson has 5 years service time, he could have refused the option and become a free agent, but he agreed to the assignment, apparently hoping that he'll get another shot when rosters expand in September.
I'm not entirely sure why Thompson stuck up here as long as he did, particularly given that there are guys like Erasmo and Scott Feldman whom you would think the Rangers would want to get a look at in the pen.