The 23-year-old, who competed in the recent COSAFA Cup in Polokwane, was formerly on the books of Windhoek-based outfit Orlando Pirates.
Cosmos recruited Hanamib as a replacement for Thapelo Tlabakwe, who joined Absa Premiership side Chippa United earlier this month.
Jomo Sono's side are expected to challenge for promotion again after coming up short in the play-offs, which were won by Black Leopards last term.