The American midfielder has returned to the States to join the MLS Cup holders.
The California-native, 22, signed for West Ham in 2009 after impressing Hammers scouts while starring for local club Sporting Santa Clara, but never managed to make a Premier League appearance during his time at Upton Park.
His lone professional outing came in the infamous 5-0 FA Cup defeat to Nottingham Forest in 2014, while he made the first-team bench once this season for November’s 2-1 loss at Everton.
The US Under-23 international was set to be out of contract in the summer but will now make an immediate move to LA upon receipt of his International Transfer Certificate, with the Galaxy acquiring his league rights from the New England Revolution, who held a discovery claim on him, in exchange for $50,000 in Allocation Money.
Speaking to the club’s official website, head coach Bruce Arena said: “Sebastian is a young, talented attacking player who we think can find success in our team.
“We’re happy to have him return to his home state to join the Galaxy and we look forward to his contributions going forward.”
After winning three of the past four MLS Cup titles under Arena’s guidance, LA were hit hard with a couple of significant offseason loses, with US soccer legend Landon Donovan’s retirement preceding the trade of midfield stalwart Marcelo Sarvas to the Colorado Rapids.
The latter move was made in anticipation of Steven Gerrard’s pre-agreed summer arrival from Liverpool but, in the meantime, the club have been working to both find a stopgap for the Reds skipper and fill Donovan’s place in the line-up.
Lletget, who will now link up with former Hammers striker and LA captain Robbie Keane, could fill either spot and will now get a chance to show his US national team credentials with some regular first-team minutes, having long-been considered a promising prospect for Jurgen Klinsmann’s plans.