The Jamaica international, who's scored 55 goals in 203 appearances since joining from Nottingham Forest in 2015, has become irreplaceable for the Hammers and the club will have the option to extend his contract by a further year.
Reborn as an out-and-out striker, the 31-year-old has been a revelation under David Moyes and perhaps symbolic of the superb progress the east London club has made under the Scot.
His goals in the latter half of the 2020/21 campaign were invaluable in the Hammers' successful quest for European football.
He has continued in the same vein this season with ten goals already at the halfway point of the season.
"We've extended one or two contracts behind the scenes," Moyes said of Antonio's new deal.
"We did Michail's contract about two months ago, but we've also done another couple of players. We've gone about our business quietly, trying to do things behind the scenes and trying to do things correctly."
Antonio recently returned from a period of self-isolation after testing positive for coronavirus.
He has become a cult hero among West ham fans - and rightly too as he is now in the top six in Premier League appearances, goals, assists, and wins in the club's 25-year history in the competition.
He also netted the club's first-ever UEFA Europa League group-stage goal earlier this season against Dinamo Zagreb in September 2021, whilst his performances have seen him recognised at international level as he's become a fully-fledged member of Jamaica's national team.
Moyes revealed there are further cases in the Hammers camp ahead of Sunday's FA Cup third-round visit of Leeds.
"Like everybody else, we've got a few," he added. "We've done very well at present with it, but I'm sure like everybody else, there's one or two.
"Other than that, we're looking forward to the game and trying to get the players and everybody ready."
The Hammers have a rearranged Premier League match against Norwich on Wednesday night, which Moyes says could force him to pick some fringe players against Leeds.
"I might do," he said. "I'm not really sure yet exactly which way we want to go.
"I think because the Premier League have put the game on Wednesday night, that's changed the whole dynamics of this FA Cup tie.
"We've been given a tough third-round draw, but we had a real tough go in the Carabao Cup too. We've done well in those games and we hope we can do well against Leeds United."