The deal was confirmed on Friday by the Besiktas Twitter feed. Per Emre Sarigul of Turkish Football, the club president Fikret Orman revealed the deal in a press conference.
"We have loaned Gokhan Tore to West Ham, they made an offer, and it appealed to us," he said. "We have a lot of competition for a place on the right wing with Andreas Beck, Gokhan Gonul, Kerim Frei, Ricardo Quaresma, Aras Ozbiliz and Olcay Sahan."
According to a report from Sky Sports, the Hammers will have the option to make this switch a permanent one should they wish.