The 6-foot-9 standout is a proven winner in the junior ranks, having won two state championships for Volcano Vista High School in Albuquerque, New Mexico.
UP Men's Basketball Team (UPMBT) director for operations Bo Perasol bared Alter's formal commitment to the squad on Sunday.
"There is a shared belief in what we are working to accomplish in UP, and we are humbled that Sean is going to be part of a team that is committed to upholding the values of our university," said Perasol in a post on Nowhere to Go But UP's Facebook page.
Alter's recruitment came just days after the UP Maroons announced that they have secured the commitment of the trio of Luis Pablo, Seven Gagate and Joshua Coronel from NCAA juniors runner-up La Salle Greenhills.
UP coach Goldwin Monteverde underscored the significance of signing "a player with the work ethic and the desire to win displayed by Sean."
Alter already began his Philippine basketball career with Fil-Nation Select in the 2023 Smart-NBTC Division 1 National Finals — averaging 5.7 points, three boards, and one dime in the team's unbeaten run thus far.
Alter's 6-foot-11 wingspan and acclaimed versatility will prove to be vital in the Maroons' hunt for a second UAAP crown in three seasons.