The quartet's contracts all expire at the end of the 2022/23 season, and will be looking for new clubs.
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All four players won all seven trophies on offer during Jurgen Klopp's reign, departing with Premier League and Champions League winners medals.
The club said in a statement: "With the visit of Aston Villa on Saturday being the Reds' final home fixture of the campaign, special acknowledgements will be paid to the quartet at Anfield, with further tributes to follow across the club's digital platforms after the end of the season as we wish Roberto, Naby, James, Alex and their families the very best for the future."
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All four players will depart with our gratitude and appreciation for the contribution they have made."
talkSPORT understands that James Milner will be joining Brighton as a free agent, with the remaining three players' futures are still undecided.
Firmino will be the most emotional departure for many fans, and particularly manager Jurgen Klopp.
He has used the Brazilian forward more than any other player during his entire management career at Liverpool, Borussia Dortmund and Mainz.
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For Keita, a £52.75million signing from RB Leipzig in 2018, his options remain open and a return to Germany could be on the cards.
Meanwhile, earlier this year, ex-Arsenal midfielder Oxlade Chamberlain was linked with Brighton, Aston Villa and Newcastle.