Rice's move to Arsenal is imminent, with the Gunners set to fork out £105m for the 24-year-old.
The England international has made 245 appearances for West Ham in total and captained the Hammers to Europa Conference League glory last month.
A statement from West Ham on Saturday morning read: "West Ham United can confirm that agreement has been reached for Declan Rice to leave the Club for a British record transfer fee.
"The 24-year-old England midfielder leaves the Hammers having made a total of 245 senior appearances for the Club – the last of which finished in glory last month as he lifted the UEFA Europa Conference League trophy in Prague to end our 43-year wait for a major honour.
"Winner of the Hammer of the Year award three times, in 2020, 2022 and 2023, and runner-up in 2018 and 2019, Declan made his full England debut in March 2019 and has since gone on to win 43 caps.
"He was named West Ham United Club Captain in the summer of 2022 following the retirement of Mark Noble and enjoyed a triumphant final season as David Moyes’s team secured only the second major European trophy in the Club’s history.
West Ham joint-chair David Sullivan has also paid tribute to Rice, saying: “I am sorry to see Declan leave us, but I believe that everyone at West Ham United should be very proud of the part we have played in his journey from the Academy of Football at Chadwell Heath to becoming the most valuable young player in English football.
“I would like to make it clear to our supporters that we did not want to sell Declan. We wanted to build our team around him and made a series of improved, long-term contract offers to secure his future. However, once Declan made it clear that he wished to move on and seek a new challenge, the Club felt it would not be right to stand in his way, acting in the best interests of West Ham United.
“He leaves with the sincere thanks, respect and love of everyone here, having earned his place in history alongside the great Bobby Moore and Billy Bonds as the only players to have captained West Ham United to a major trophy. More than that, he has always given absolutely everything for the football club throughout his time with us.
“Declan will forever hold a special place in the hearts of Hammers fans and everyone here at the Club. We wish him well for the future and he will always be an inspiration and an example to any young player coming through our Academy.”
