Landers will team up with the Academy following a successful trial period at Rush Green Training Ground with Mark Robson’s side. The 17-year-old made three appearances for Hibs, the last of them a year ago.
Sporting director Malky Mackay admitted it was difficult to stop Landers leaving when the call from the Hammers came.
"From a club perspective, we are pleased with the level of compensation we have received for Josh," Mackay added.
"We are proud that our academy has produced another player fit for an English Premier League side.
"Of course, the main aim for our academy is to produce players for our own first team, however, when a move like this comes up - it is difficult to deny a youngster that opportunity.
Landers has been with the Hibernian’s academy since he was ten years old but now begins the next stage of his development in Claret and Blue under manager Graham Potter who will be keeping a close eye on his development.