The ongoing Thrift Savings Plan open season, which started May 15 and ends July 31, will be the last under the cycle the TSP has used since its inception more than a decade ago. Instead of the next open season occurring November 15 and running through next January 31, the fall open seasons beginning with the upcoming one will run October 15-December 31. The spring open seasons will start April 15 and end June 30. During open season employees may change the levels of their investments and those not participating in the program may join it.