Commercial Orbital Transportation Services
STS-135 delivered supplies and equipment to provision the space station through 2012, following the end of NASA's Space Shuttle program. Since the ISS program was extended to 2024 (now 2030), the station is resupplied by the Commercial Orbital Transportation Services program which took over resupply missions from the Shuttle. A shuttle extension beyond STS-135 wasn't seriously considered, and an ISS extension was never intended to be a guaranteed shuttle program extension, and the Shuttle program officially ended after STS-135.