Fijian scrum-half Matawalu first joined in 2012 and is in his second spell with Glasgow where he is a hugely popular figure.
He was voted the club’s player of the season in 2013 and 2015 and has scored 44 tries – only DTH van der Merwe and Seymour have more.
“When I first joined Glasgow Warriors in 2012 the biggest thing that stood out to me was the culture that the players created; I loved how the club had clans, traditions and customs – all like Fiji,” Matawalu, 32, said.
“Glasgow is my second home and I feel an immense sense of pride to have been part of this wonderful club.
“I’m ready to experience something new outside of Glasgow but I will miss and look back fondly on my time working and playing with all of my babies.”
Harrogate-born prop Allan joined Glasgow in 2014 and earned eight caps for Scotland.
“I am immensely proud to have represented Glasgow Warriors,” the 29-year-old said.
“There have been some incredible moments over the last seven years both on and off the pitch.”
Glasgow Warriors head coach Danny Wilson added: “Niko and Alex have both been fantastic servants to the club.
“They depart as centurions and should be celebrated for their achievements. Both are good club men and we wish them all the best for the future.”