Aki has been an influential figure in the Irish squad since making his debut in 2017 after qualifying through the residency rule.
He has won 69 caps for Ireland, three Six Nations titles and in 2023 was nominated for the World Rugby Player of the Year award.
The 35-year-old missed the first three games of the Six Nations after receiving a four-game suspension for “verbal abuse and disrespect” towards match officials following Connacht’s loss to Leinster earlier this year.
Van der Flier, 32, who was the 2022 World Rugby Player of the Year, has committed his future after recapturing his best form during the Six Nations.
Gibson-Park, who won his 50th Ireland cap against Wales earlier this month, has also signed on until 2028.
The 34-year-old scrum-half enjoyed an excellent Six Nations and was player of the match in Ireland’s thumping 42-21 win over England at Twickenham last month.
Sheehan, meanwhile, has emerged as one of Ireland’s most consistent players since debuting at Test level in 2021.
The 27-year-old has scored 18 tries in 39 caps and captained Ireland in last year’s Triple Crown-sealing win over Wales in Caelan Doris’ absence.
“You cannot underestimate the outstanding contributions of these four players to Irish rugby over many years,” said head coach Andy Farrell.
“That they see their futures here is a significant boost, which I have no doubt will delight Ireland supporters around the world.
“They are all key leaders who put their bodies on the line time and time again in reaching the highest standards on the field.”
