Although the official report from the Hammers claims he has joined for an undisclosed fee, it is understood the 25-year-old cost the club around £35 million.
Alvarez has signed a five-year deal with the Europa Conference League winners, keeping him at London Stadium until 2028.
West Ham have shrugged off competition from several European giants, including Bayern Munich and Borussia Dortmund, to land Alvarez’s signature.
The Gold Cup winner becomes the first signing of the summer transfer window to join David Moyes’ side, but the Scottish manager will hope for more new faces.
Alvarez is a like-for-like replacement for Declan Rice and could prove a shrewd acquisition by the Hammers, considering the player’s performances for club and country over the years.
“I am very happy and very proud to be here,” said Alvarez. “Being here in London and seeing London Stadium – it’s amazing. I can’t wait to play here in front of the West Ham fans.
“The Premier League is a special league, the best league in the world, and I think my style will suit it. I now have a responsibility to West Ham and the West Ham family, and I will give absolutely everything for the shirt.”
Moyes is hoping to welcome another two new players, with West Ham close to signing Manchester United defender Harry Maguire and Southampton midfielder James Ward-Prowse.
The Hammers have agreed deals to sign both players, and all that remains is an agreement on personal terms, although that is not expected to be a problem.
West Ham are determined to improve on their 2022/23 domestic campaign after finishing 14th in the Premier League table.
Their European success did enough to cloud the domestic disappointment, but they will be desperate to return to the top half of the table this season.
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